security hardening (#12)

Reviewed-on: #12
Co-authored-by: Cedric Hornberger <ceddi.hornberger@gmx.de>
Co-committed-by: Cedric Hornberger <ceddi.hornberger@gmx.de>

.gitea/workflows/tag_release.yml

@@ -2,8 +2,8 @@ name: Build and Deploy Versioned Spring Boot Server
 
 on:
   push:
-    tags: # Match all tags
-      - "*"
+    tags:
+      - "*" # Match all tags
 
 jobs:
   build:
@@ -43,20 +43,42 @@ jobs:
       - name: Extract Tag Version
         id: extract_version
         run: |
-          TAG_VERSION=${GITEA_REF#refs/tags/}
+          TAG_VERSION=$(echo "${GITHUB_REF}" | sed 's#refs/tags/##')
+          if [ -z "$TAG_VERSION" ]; then
+            echo "Error: TAG_VERSION is empty."
+            exit 1
+          fi
           echo "TAG_VERSION=$TAG_VERSION" >> $GITHUB_ENV
 
+          # Extract major and minor versions
+          MAJOR_VERSION=$(echo "${TAG_VERSION}" | cut -d. -f1)
+          MINOR_VERSION=$(echo "${TAG_VERSION}" | cut -d. -f1,2)
+          echo "MAJOR_VERSION=$MAJOR_VERSION" >> $GITHUB_ENV
+          echo "MINOR_VERSION=$MINOR_VERSION" >> $GITHUB_ENV
+
       # 7. Build the Docker image with the tag
       - name: Build and Package Docker Image
         run: |
           docker build -t tea.zendric.de/cedric/xpensely-server:${{ env.TAG_VERSION }} .
 
-      # 8. Docker login
+      # 8. Tag the image with Major Version (e.g., 0)
+      - name: Tag with Major Version
+        run: |
+          docker tag tea.zendric.de/cedric/xpensely-server:${{ env.TAG_VERSION }} tea.zendric.de/cedric/xpensely-server:${{ env.MAJOR_VERSION }}
+
+      # 9. Tag the image with Minor Version (e.g., 0.1)
+      - name: Tag with Minor Version
+        run: |
+          docker tag tea.zendric.de/cedric/xpensely-server:${{ env.TAG_VERSION }} tea.zendric.de/cedric/xpensely-server:${{ env.MINOR_VERSION }}
+
+      # 10. Docker login
       - name: Login to Docker Registry
         run: |
           echo "${{ secrets.TEAPASSWORD }}" | docker login tea.zendric.de -u ${{ secrets.TEAUSER }} --password-stdin
 
-      # 9. Push the Docker image with the tag
+      # 11. Push the Docker images with the tags
       - name: Push the Docker Image to registry
         run: |
           docker push tea.zendric.de/cedric/xpensely-server:${{ env.TAG_VERSION }}
+          docker push tea.zendric.de/cedric/xpensely-server:${{ env.MAJOR_VERSION }}
+          docker push tea.zendric.de/cedric/xpensely-server:${{ env.MINOR_VERSION }}

.gitignore

@@ -1,5 +1,6 @@
 HELP.md
 target/
+/docs/superpowers
 !.mvn/wrapper/maven-wrapper.jar
 !**/src/main/**/target/
 !**/src/test/**/target/

docker-compose.yml

@@ -1,42 +1,43 @@
-version: "3.8"
 services:
   xpensely-server:
     image: tea.zendric.de/cedric/xpensely-server:latest
-    container_name: xpensely-server
-    ports:
-      - 3636:8080
+    restart: always
     environment:
       GOOGLE_CLIENT_ID: ${GOOGLE_CLIENT_ID}
       GOOGLE_CLIENT_SECRET: ${GOOGLE_CLIENT_SECRET}
-      DB_PORT: 5434
-      DB_NAME: ${DB_P_NAME}
-      DB_USERNAME: ${DB_USERNAME}
-      DB_PASSWORD: ${DB_PASSWORD}
+
+      DB_PORT: 5432
+      DB_P_NAME: ${POSTGRES_DB}
+      DB_USERNAME: ${POSTGRES_USER}
+      DB_PASSWORD: ${POSTGRES_PASSWORD}
+
+      SPRING_PROFILES_ACTIVE: ${SPRING_PROFILES_ACTIVE}
     depends_on:
       postgresdb:
         condition: service_healthy
     networks:
       - xpensely-network
+
   postgresdb:
     image: postgres:14
-    container_name: postgresdb
-    ports:
-      - 5434:5432
+    restart: unless-stopped
     environment:
-      POSTGRES_DB: ${DB_P_NAME}
-      POSTGRES_USER: ${DB_USERNAME}
-      POSTGRES_PASSWORD: ${DB_PASSWORD}
+      POSTGRES_DB: ${POSTGRES_DB}
+      POSTGRES_USER: ${POSTGRES_USER}
+      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD}
+    volumes:
+      - postgres_data:/var/lib/postgresql/data
     networks:
       - xpensely-network
-    volumes:
-      - db_data:/var/lib/postgresql/data
-    restart: unless-stopped
     healthcheck:
-      test: ["CMD-SHELL", "pg_isready -U ${DB_USERNAME}"]
+      test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER} -d ${POSTGRES_DB}"]
       interval: 10s
       timeout: 5s
       retries: 5
+
 volumes:
-  db_data: null
+  postgres_data:
+
 networks:
-  xpensely-network: null
+  xpensely-network:
+    driver: bridge

dockerfile

@@ -1,7 +1,7 @@
-FROM openjdk:17-jdk-slim
+FROM eclipse-temurin:17-jdk
 
 COPY ./target/*.jar app.jar
 
 EXPOSE 8080
 
-ENTRYPOINT ["java", "-jar", "app.jar"]
+ENTRYPOINT ["java","-jar", "app.jar"]

pom.xml

@@ -27,7 +27,7 @@
 		<url/>
 	</scm>
 	<properties>
-		<java.version>17</java.version>
+		<java.version>21</java.version>
 	</properties>
 	<dependencies>
 		<dependency>
@@ -38,6 +38,15 @@
 			<groupId>org.springframework.boot</groupId>
 			<artifactId>spring-boot-starter-security</artifactId>
 		</dependency>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-validation</artifactId>
+		</dependency>
+		<dependency>
+			<groupId>com.bucket4j</groupId>
+			<artifactId>bucket4j-core</artifactId>
+			<version>8.10.1</version>
+		</dependency>
 		<dependency>
         	<groupId>org.springframework.boot</groupId>
         	<artifactId>spring-boot-starter-oauth2-resource-server</artifactId>
@@ -71,6 +80,11 @@
 			<artifactId>spring-boot-starter-test</artifactId>
 			<scope>test</scope>
 		</dependency>
+		<dependency>
+			<groupId>com.h2database</groupId>
+			<artifactId>h2</artifactId>
+			<scope>test</scope>
+		</dependency>
 		<dependency>
 			<groupId>org.springframework.security</groupId>
 			<artifactId>spring-security-test</artifactId>

src/main/java/de/zendric/app/xpensely_server/controller/AppUserController.java

@@ -1,35 +1,35 @@
 package de.zendric.app.xpensely_server.controller;
 
-import org.springframework.beans.factory.annotation.Autowired;
+import jakarta.validation.Valid;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
-import org.springframework.web.bind.annotation.DeleteMapping;
-import org.springframework.web.bind.annotation.GetMapping;
-import org.springframework.web.bind.annotation.PostMapping;
-import org.springframework.web.bind.annotation.RequestBody;
-import org.springframework.web.bind.annotation.RequestMapping;
-import org.springframework.web.bind.annotation.RequestParam;
-import org.springframework.web.bind.annotation.RestController;
+import org.springframework.security.core.Authentication;
+import org.springframework.web.bind.annotation.*;
+import org.springframework.web.server.ResponseStatusException;
 
 import de.zendric.app.xpensely_server.model.AppUser;
 import de.zendric.app.xpensely_server.model.AppUserCreateRequest;
-import de.zendric.app.xpensely_server.model.UsernameAlreadyExistsException;
+import de.zendric.app.xpensely_server.model.Exception.UsernameAlreadyExistsException;
+import de.zendric.app.xpensely_server.security.AuthenticatedUserResolver;
 import de.zendric.app.xpensely_server.services.UserService;
 
 @RestController
 @RequestMapping("/api/users")
 public class AppUserController {
 
-    private UserService userService;
+    private final UserService userService;
+    private final AuthenticatedUserResolver authenticatedUserResolver;
 
-    @Autowired
-    public AppUserController(UserService userService) {
+    public AppUserController(UserService userService, AuthenticatedUserResolver authenticatedUserResolver) {
         this.userService = userService;
+        this.authenticatedUserResolver = authenticatedUserResolver;
     }
 
     @GetMapping
-    public AppUser getUser(@RequestParam Long id) {
-        return userService.getUser(id);
+    public ResponseEntity<AppUser> getUser(@RequestParam Long id, Authentication authentication) {
+        AppUser self = authenticatedUserResolver.resolveCurrentUser(authentication);
+        assertSelf(self, id);
+        return ResponseEntity.ok(userService.getUser(id));
     }
 
     @GetMapping("/byName")
@@ -38,23 +38,17 @@ public class AppUserController {
     }
 
     @GetMapping("/byGoogleId")
-    public ResponseEntity<AppUser> getUserByGoogleId(@RequestParam String id) {
-        try {
-            AppUser userByGoogleId = userService.getUserByGoogleId(id);
-            return new ResponseEntity<>(userByGoogleId, HttpStatus.OK);
-
-        } catch (IllegalArgumentException e) {
-            return new ResponseEntity<>(null, HttpStatus.BAD_REQUEST);
-        } catch (Exception e) {
-            return new ResponseEntity<>(null, HttpStatus.INTERNAL_SERVER_ERROR);
-        }
+    public ResponseEntity<AppUser> getUserByGoogleId(@RequestParam String id, Authentication authentication) {
+        AppUser self = authenticatedUserResolver.resolveCurrentUser(authentication);
+        if (!self.getGoogleId().equals(id))
+            throw new ResponseStatusException(HttpStatus.FORBIDDEN);
+        return ResponseEntity.ok(self);
     }
 
     @PostMapping("/createUser")
-    public ResponseEntity<AppUser> createUser(@RequestBody AppUserCreateRequest userRequest) {
+    public ResponseEntity<AppUser> createUser(@RequestBody @Valid AppUserCreateRequest userRequest) {
         try {
             AppUser convertedUser = userRequest.convertToAppUser();
-
             AppUser nUser = userService.createUser(convertedUser);
             return new ResponseEntity<>(nUser, HttpStatus.CREATED);
         } catch (UsernameAlreadyExistsException e) {
@@ -62,12 +56,18 @@ public class AppUserController {
         } catch (Exception e) {
             return new ResponseEntity<>(null, HttpStatus.BAD_REQUEST);
         }
-
     }
 
     @DeleteMapping
-    public String deleteUser(@RequestParam Long id) {
+    public ResponseEntity<String> deleteUser(@RequestParam Long id, Authentication authentication) {
+        AppUser self = authenticatedUserResolver.resolveCurrentUser(authentication);
+        assertSelf(self, id);
         AppUser user = userService.deleteUserById(id);
-        return "User deleted : " + user.getUsername();
+        return ResponseEntity.ok("User deleted: " + user.getUsername());
+    }
+
+    private void assertSelf(AppUser authenticated, Long requestedId) {
+        if (!authenticated.getId().equals(requestedId))
+            throw new ResponseStatusException(HttpStatus.FORBIDDEN);
     }
 }

src/main/java/de/zendric/app/xpensely_server/controller/ExpenseListController.java

@@ -1,117 +1,71 @@
 package de.zendric.app.xpensely_server.controller;
 
 import java.time.LocalDateTime;
-import java.util.ArrayList;
 import java.util.List;
 import java.util.Optional;
 
-import org.springframework.beans.factory.annotation.Autowired;
+import jakarta.validation.Valid;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
-import org.springframework.web.bind.annotation.DeleteMapping;
-import org.springframework.web.bind.annotation.GetMapping;
-import org.springframework.web.bind.annotation.PathVariable;
-import org.springframework.web.bind.annotation.PostMapping;
-import org.springframework.web.bind.annotation.PutMapping;
-import org.springframework.web.bind.annotation.RequestBody;
-import org.springframework.web.bind.annotation.RequestMapping;
-import org.springframework.web.bind.annotation.RequestParam;
-import org.springframework.web.bind.annotation.RestController;
+import org.springframework.security.core.Authentication;
+import org.springframework.web.bind.annotation.*;
+import org.springframework.web.server.ResponseStatusException;
 
-import de.zendric.app.xpensely_server.model.AppUser;
-import de.zendric.app.xpensely_server.model.Expense;
-import de.zendric.app.xpensely_server.model.ExpenseChangeRequest;
-import de.zendric.app.xpensely_server.model.ExpenseInput;
-import de.zendric.app.xpensely_server.model.ExpenseList;
-import de.zendric.app.xpensely_server.model.InviteRequest;
+import de.zendric.app.xpensely_server.model.*;
+import de.zendric.app.xpensely_server.security.AuthenticatedUserResolver;
+import de.zendric.app.xpensely_server.services.CategoryService;
 import de.zendric.app.xpensely_server.services.ExpenseListService;
 import de.zendric.app.xpensely_server.services.UserService;
 
 @RestController
 @RequestMapping("/api/expenselist")
-class ExpenseListController {
+public class ExpenseListController {
 
-    private ExpenseListService expenseListService;
-    private UserService userService;
+    private final ExpenseListService expenseListService;
+    private final UserService userService;
+    private final CategoryService categoryService;
+    private final AuthenticatedUserResolver authenticatedUserResolver;
 
-    @Autowired
-    public ExpenseListController(ExpenseListService expenseListService, UserService userService) {
+    public ExpenseListController(ExpenseListService expenseListService, UserService userService,
+            CategoryService categoryService, AuthenticatedUserResolver authenticatedUserResolver) {
         this.expenseListService = expenseListService;
         this.userService = userService;
+        this.categoryService = categoryService;
+        this.authenticatedUserResolver = authenticatedUserResolver;
     }
 
-    @GetMapping("/all")
-    public ResponseEntity<List<ExpenseList>> getAll() {
-        try {
-            List<ExpenseList> items = new ArrayList<>();
-
-            expenseListService.findAll().forEach(items::add);
-
-            if (items.isEmpty())
-                return new ResponseEntity<>(HttpStatus.NO_CONTENT);
-
-            return new ResponseEntity<>(items, HttpStatus.OK);
-        } catch (Exception e) {
-            return new ResponseEntity<>(null, HttpStatus.INTERNAL_SERVER_ERROR);
-        }
-    }
-
-    @GetMapping("/byUser")
-    public ResponseEntity<List<ExpenseList>> getByUser(@RequestParam Long userId) {
-        try {
-            List<ExpenseList> items = expenseListService.findByUserId(userId);
-
-            if (items.isEmpty())
-                return new ResponseEntity<>(HttpStatus.NO_CONTENT);
-
-            return new ResponseEntity<>(items, HttpStatus.OK);
-        } catch (Exception e) {
-            return new ResponseEntity<>(null, HttpStatus.INTERNAL_SERVER_ERROR);
-        }
-    }
-
-    @GetMapping("/byUsername")
-    public ResponseEntity<List<ExpenseList>> getByUser(@RequestParam String username) {
-        try {
-            List<ExpenseList> items = expenseListService.findByUsername(username);
-
-            if (items.isEmpty())
-                return new ResponseEntity<>(HttpStatus.NO_CONTENT);
-
-            return new ResponseEntity<>(items, HttpStatus.OK);
-        } catch (Exception e) {
-            return new ResponseEntity<>(null, HttpStatus.INTERNAL_SERVER_ERROR);
-        }
+    @GetMapping("/mine")
+    public ResponseEntity<List<ExpenseList>> getMine(Authentication authentication) {
+        AppUser user = authenticatedUserResolver.resolveCurrentUser(authentication);
+        List<ExpenseList> items = expenseListService.findByUserId(user.getId());
+        if (items.isEmpty())
+            return new ResponseEntity<>(HttpStatus.NO_CONTENT);
+        return new ResponseEntity<>(items, HttpStatus.OK);
     }
 
     @GetMapping("/byId")
-    public ResponseEntity<ExpenseList> getById(@RequestParam Long id) {
+    public ResponseEntity<ExpenseList> getById(@RequestParam Long id, Authentication authentication) {
+        AppUser user = authenticatedUserResolver.resolveCurrentUser(authentication);
         Optional<ExpenseList> existingItemOptional = expenseListService.findById(id);
-
-        if (existingItemOptional.isPresent()) {
-            return new ResponseEntity<>(existingItemOptional.get(), HttpStatus.OK);
-        } else {
+        if (existingItemOptional.isEmpty())
             return new ResponseEntity<>(HttpStatus.NOT_FOUND);
-        }
+        assertMember(user, existingItemOptional.get());
+        return new ResponseEntity<>(existingItemOptional.get(), HttpStatus.OK);
     }
 
     @PostMapping("/create")
-    public ResponseEntity<ExpenseList> create(@RequestBody ExpenseList expenseList) {
+    public ResponseEntity<ExpenseList> create(@RequestBody ExpenseList expenseList,
+            Authentication authentication) {
         try {
-            if (expenseList.getOwner() != null) {
-                AppUser existingOwner = userService.getUser(expenseList.getOwner().getId());
-                if (existingOwner == null) {
-                    throw new IllegalArgumentException("Owner does not exist.");
-                }
-                expenseList.setOwner(existingOwner);
-            } else {
-                throw new IllegalArgumentException("Owner is required.");
-            }
-
+            AppUser authenticatedUser = authenticatedUserResolver.resolveCurrentUser(authentication);
+            expenseList.setOwner(authenticatedUser);
+            XpenselyStandardCategories standardCategories = categoryService.getDefaultCategories();
+            expenseList.setXpenselyStandardCategories(standardCategories);
             expenseList.setSharedWith(null);
-
             ExpenseList savedItem = expenseListService.createList(expenseList);
             return new ResponseEntity<>(savedItem, HttpStatus.CREATED);
+        } catch (ResponseStatusException e) {
+            throw e;
         } catch (Exception e) {
             e.printStackTrace();
             return new ResponseEntity<>(null, HttpStatus.EXPECTATION_FAILED);
@@ -119,7 +73,12 @@ class ExpenseListController {
     }
 
     @DeleteMapping("{id}")
-    public ResponseEntity<HttpStatus> delete(@PathVariable("id") Long id) {
+    public ResponseEntity<HttpStatus> delete(@PathVariable("id") Long id, Authentication authentication) {
+        AppUser user = authenticatedUserResolver.resolveCurrentUser(authentication);
+        Optional<ExpenseList> listOpt = expenseListService.findById(id);
+        if (listOpt.isEmpty())
+            return new ResponseEntity<>(HttpStatus.NOT_FOUND);
+        assertOwner(user, listOpt.get());
         try {
             expenseListService.deleteById(id);
             return new ResponseEntity<>(HttpStatus.NO_CONTENT);
@@ -131,11 +90,16 @@ class ExpenseListController {
     @PostMapping("/{id}/add")
     public ResponseEntity<Expense> addExpenseToList(
             @PathVariable("id") Long expenseListId,
-            @RequestBody ExpenseInput expenseInput) {
+            @RequestBody @Valid ExpenseInput expenseInput,
+            Authentication authentication) {
+        AppUser user = authenticatedUserResolver.resolveCurrentUser(authentication);
+        Optional<ExpenseList> listOpt = expenseListService.findById(expenseListId);
+        if (listOpt.isEmpty())
+            return new ResponseEntity<>(HttpStatus.NOT_FOUND);
+        assertMember(user, listOpt.get());
         try {
             AppUser expenseOwner = userService.getUserByName(expenseInput.getOwner());
             Expense expense = expenseInput.convertToExpense(expenseOwner.getId());
-
             Expense addedExpense = expenseListService.addExpenseToList(expenseListId, expense);
             return new ResponseEntity<>(addedExpense, HttpStatus.CREATED);
         } catch (Exception e) {
@@ -146,18 +110,18 @@ class ExpenseListController {
     @PutMapping("/{id}/update")
     public ResponseEntity<Expense> updateExpenseInList(
             @PathVariable("id") Long expenseListId,
-            @RequestBody ExpenseChangeRequest expenseChangeRequest) {
+            @RequestBody @Valid ExpenseChangeRequest expenseChangeRequest,
+            Authentication authentication) {
+        AppUser user = authenticatedUserResolver.resolveCurrentUser(authentication);
+        Optional<ExpenseList> expenseListOpt = expenseListService.findById(expenseListId);
+        if (expenseListOpt.isEmpty())
+            return new ResponseEntity<>(null, HttpStatus.NOT_FOUND);
+        assertMember(user, expenseListOpt.get());
         try {
             AppUser expenseOwner = userService.getUserByName(expenseChangeRequest.getOwnerName());
-            Optional<ExpenseList> expenseList = expenseListService.findById(expenseListId);
-            if (expenseList.isPresent()) {
-                Expense expense = expenseChangeRequest.convertToExpense(expenseOwner.getId(), expenseList.get());
-
-                Expense addedExpense = expenseListService.updateExpense(expenseListId, expense);
-                return new ResponseEntity<>(addedExpense, HttpStatus.CREATED);
-            }
-            return new ResponseEntity<>(null, HttpStatus.BAD_REQUEST);
-
+            Expense expense = expenseChangeRequest.convertToExpense(expenseOwner.getId(), expenseListOpt.get());
+            Expense updatedExpense = expenseListService.updateExpense(expenseListId, expense);
+            return new ResponseEntity<>(updatedExpense, HttpStatus.OK);
         } catch (Exception e) {
             return new ResponseEntity<>(null, HttpStatus.BAD_REQUEST);
         }
@@ -166,7 +130,13 @@ class ExpenseListController {
     @DeleteMapping("/{id}/delete")
     public ResponseEntity<Expense> deleteExpenseFromList(
             @PathVariable("id") Long expenseListId,
-            @RequestParam("expenseId") Long expenseId) {
+            @RequestParam("expenseId") Long expenseId,
+            Authentication authentication) {
+        AppUser user = authenticatedUserResolver.resolveCurrentUser(authentication);
+        Optional<ExpenseList> listOpt = expenseListService.findById(expenseListId);
+        if (listOpt.isEmpty())
+            return new ResponseEntity<>(HttpStatus.NOT_FOUND);
+        assertMember(user, listOpt.get());
         try {
             expenseListService.deleteExpenseFromList(expenseListId, expenseId);
             return new ResponseEntity<>(HttpStatus.NO_CONTENT);
@@ -176,13 +146,20 @@ class ExpenseListController {
     }
 
     @PostMapping("/{listId}/invite")
-    public ResponseEntity<String> generateInvite(@PathVariable Long listId) {
+    public ResponseEntity<String> generateInvite(@PathVariable Long listId, Authentication authentication) {
+        AppUser user = authenticatedUserResolver.resolveCurrentUser(authentication);
+        Optional<ExpenseList> listOpt = expenseListService.findById(listId);
+        if (listOpt.isEmpty())
+            return new ResponseEntity<>(HttpStatus.NOT_FOUND);
+        assertOwner(user, listOpt.get());
         String inviteCode = expenseListService.generateInviteCode(listId);
         return ResponseEntity.ok(inviteCode);
     }
 
     @PostMapping("/accept-invite")
-    public ResponseEntity<?> acceptInvite(@RequestBody InviteRequest inviteRequest) {
+    public ResponseEntity<?> acceptInvite(@RequestBody @Valid InviteRequest inviteRequest,
+            Authentication authentication) {
+        AppUser authenticatedUser = authenticatedUserResolver.resolveCurrentUser(authentication);
         ExpenseList list = expenseListService.findByInviteCode(inviteRequest.getInviteCode());
 
         if (list == null || list.getInviteCodeExpiration() == null ||
@@ -192,21 +169,24 @@ class ExpenseListController {
         if (list.getSharedWith() != null) {
             return ResponseEntity.status(HttpStatus.IM_USED).body("List has already been shared");
         }
-        if (list.getOwner().getId() == inviteRequest.getUserId()) {
-            return ResponseEntity.status(HttpStatus.BAD_REQUEST).body("You cant join your own List");
-        }
-        AppUser user = null;
-        try {
-            user = userService.getUser(inviteRequest.getUserId());
-        } catch (Exception e) {
-            throw new RuntimeException("User not found");
-        }
-        if (user != null) {
-            list.setSharedWith(user);
-            expenseListService.save(list);
-        } else {
-            throw new RuntimeException("User not found");
+        if (list.getOwner().getId().equals(authenticatedUser.getId())) {
+            return ResponseEntity.status(HttpStatus.BAD_REQUEST).body("You cannot join your own list");
         }
+        list.setSharedWith(authenticatedUser);
+        expenseListService.save(list);
         return ResponseEntity.ok("User added to the list");
     }
+
+    private void assertOwner(AppUser authenticated, ExpenseList list) {
+        if (!list.getOwner().getId().equals(authenticated.getId()))
+            throw new ResponseStatusException(HttpStatus.FORBIDDEN);
+    }
+
+    private void assertMember(AppUser authenticated, ExpenseList list) {
+        boolean isOwner = list.getOwner().getId().equals(authenticated.getId());
+        boolean isShared = list.getSharedWith() != null
+                && list.getSharedWith().getId().equals(authenticated.getId());
+        if (!isOwner && !isShared)
+            throw new ResponseStatusException(HttpStatus.FORBIDDEN);
+    }
 }

src/main/java/de/zendric/app/xpensely_server/controller/GlobalExceptionHandler.java

@@ -0,0 +1,30 @@
+package de.zendric.app.xpensely_server.controller;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.validation.FieldError;
+import org.springframework.web.bind.MethodArgumentNotValidException;
+import org.springframework.web.bind.annotation.ExceptionHandler;
+import org.springframework.web.bind.annotation.RestControllerAdvice;
+
+import java.util.HashMap;
+import java.util.Map;
+
+@RestControllerAdvice
+public class GlobalExceptionHandler {
+
+    @ExceptionHandler(MethodArgumentNotValidException.class)
+    public ResponseEntity<Map<String, String>> handleValidationErrors(MethodArgumentNotValidException ex) {
+        Map<String, String> errors = new HashMap<>();
+        for (FieldError fieldError : ex.getBindingResult().getFieldErrors()) {
+            errors.put(fieldError.getField(), fieldError.getDefaultMessage());
+        }
+        return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(errors);
+    }
+
+    @ExceptionHandler(IllegalArgumentException.class)
+    public ResponseEntity<Map<String, String>> handleIllegalArgument(IllegalArgumentException ex) {
+        return ResponseEntity.status(HttpStatus.BAD_REQUEST)
+                .body(Map.of("error", ex.getMessage()));
+    }
+}

src/main/java/de/zendric/app/xpensely_server/model/AppUserCreateRequest.java

@@ -1,21 +1,25 @@
 package de.zendric.app.xpensely_server.model;
 
-import jakarta.persistence.Column;
+import jakarta.validation.constraints.NotBlank;
+import jakarta.validation.constraints.Pattern;
+import jakarta.validation.constraints.Size;
 import lombok.Data;
 
 @Data
 public class AppUserCreateRequest {
 
-    @Column(name = "username", nullable = false, unique = true)
+    @NotBlank(message = "Username is required")
+    @Size(min = 3, max = 30, message = "Username must be between 3 and 30 characters")
+    @Pattern(regexp = "^[a-zA-Z0-9_.\\-]+$", message = "Username may only contain letters, digits, underscores, dots, and hyphens")
     private String username;
 
+    @NotBlank(message = "Google ID is required")
     private String googleId;
 
     public AppUser convertToAppUser() {
         AppUser appUser = new AppUser();
         appUser.setGoogleId(googleId);
         appUser.setUsername(username);
-
         return appUser;
     }
 }

src/main/java/de/zendric/app/xpensely_server/model/DTO/ExpenseListDTO.java

@@ -0,0 +1,8 @@
+package de.zendric.app.xpensely_server.model.DTO;
+
+public class ExpenseListDTO {
+
+    // TODO should combine the two categories to one;
+
+    // private List<CategoryDTO> availableCategories;
+}

src/main/java/de/zendric/app/xpensely_server/model/Exception/ResourceNotFoundException.java

@@ -0,0 +1,11 @@
+package de.zendric.app.xpensely_server.model.Exception;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.web.bind.annotation.ResponseStatus;
+
+@ResponseStatus(HttpStatus.NOT_FOUND)
+public class ResourceNotFoundException extends RuntimeException {
+    public ResourceNotFoundException(String message) {
+        super(message);
+    }
+}

src/main/java/de/zendric/app/xpensely_server/model/Exception/UsernameAlreadyExistsException.java

@@ -1,4 +1,4 @@
-package de.zendric.app.xpensely_server.model;
+package de.zendric.app.xpensely_server.model.Exception;
 
 import org.springframework.http.HttpStatus;
 import org.springframework.web.bind.annotation.ResponseStatus;

src/main/java/de/zendric/app/xpensely_server/model/Expense.java

@@ -34,7 +34,7 @@ public class Expense {
     private Double amount;
     private Double personalUseAmount;
     private Double otherPersonAmount;
-
+    private String category;
     private LocalDate date;
 
     @ManyToOne

src/main/java/de/zendric/app/xpensely_server/model/ExpenseChangeRequest.java

@@ -2,6 +2,10 @@ package de.zendric.app.xpensely_server.model;
 
 import java.time.LocalDate;
 
+import jakarta.validation.constraints.DecimalMin;
+import jakarta.validation.constraints.NotBlank;
+import jakarta.validation.constraints.NotNull;
+import jakarta.validation.constraints.Size;
 import lombok.AllArgsConstructor;
 import lombok.Data;
 import lombok.NoArgsConstructor;
@@ -12,13 +16,27 @@ import lombok.NoArgsConstructor;
 public class ExpenseChangeRequest {
 
     private Long id;
+
+    @NotBlank(message = "Title is required")
+    @Size(max = 100, message = "Title must not exceed 100 characters")
     private String title;
+
+    @NotBlank(message = "Owner name is required")
     private String ownerName;
+
+    @NotNull(message = "Amount is required")
+    @DecimalMin(value = "0.01", message = "Amount must be greater than zero")
     private Double amount;
+
     private Double personalUseAmount;
     private Double otherPersonAmount;
+
+    @NotNull(message = "Date is required")
     private LocalDate date;
 
+    @NotBlank(message = "Category is required")
+    private String category;
+
     public Expense convertToExpense(Long userId, ExpenseList expenseList) {
         AppUser appUser = new AppUser();
         appUser.setId(userId);
@@ -33,7 +51,8 @@ public class ExpenseChangeRequest {
         expense.setId(id);
         expense.setOwner(appUser);
         expense.setTitle(title);
+        expense.setCategory(category);
 
         return expense;
     }
-}
+}

src/main/java/de/zendric/app/xpensely_server/model/ExpenseInput.java

@@ -2,9 +2,10 @@ package de.zendric.app.xpensely_server.model;
 
 import java.time.LocalDate;
 
-import jakarta.persistence.GeneratedValue;
-import jakarta.persistence.GenerationType;
-import jakarta.persistence.Id;
+import jakarta.validation.constraints.DecimalMin;
+import jakarta.validation.constraints.NotBlank;
+import jakarta.validation.constraints.NotNull;
+import jakarta.validation.constraints.Size;
 import lombok.AllArgsConstructor;
 import lombok.Getter;
 import lombok.NoArgsConstructor;
@@ -16,20 +17,28 @@ import lombok.Setter;
 @NoArgsConstructor
 public class ExpenseInput {
 
-    @Id
-    @GeneratedValue(strategy = GenerationType.IDENTITY)
     private Long id;
 
+    @NotBlank(message = "Title is required")
+    @Size(max = 100, message = "Title must not exceed 100 characters")
     private String title;
 
+    @NotBlank(message = "Owner is required")
     private String owner;
 
+    @NotNull(message = "Amount is required")
+    @DecimalMin(value = "0.01", message = "Amount must be greater than zero")
     private Double amount;
+
     private Double personalUseAmount;
     private Double otherPersonAmount;
 
+    @NotNull(message = "Date is required")
     private LocalDate date;
 
+    @NotBlank(message = "Category is required")
+    private String category;
+
     private ExpenseList expenseList;
 
     public Expense convertToExpense(Long userId) {
@@ -46,6 +55,7 @@ public class ExpenseInput {
         expense.setId(id);
         expense.setOwner(appUser);
         expense.setTitle(title);
+        expense.setCategory(category);
 
         return expense;
     }

src/main/java/de/zendric/app/xpensely_server/model/ExpenseList.java

@@ -8,6 +8,7 @@ import com.fasterxml.jackson.annotation.JsonManagedReference;
 
 import jakarta.persistence.CascadeType;
 import jakarta.persistence.Entity;
+import jakarta.persistence.FetchType;
 import jakarta.persistence.GeneratedValue;
 import jakarta.persistence.GenerationType;
 import jakarta.persistence.Id;
@@ -40,6 +41,14 @@ public class ExpenseList {
     @ManyToOne
     private AppUser sharedWith;
 
+    @ManyToOne(fetch = FetchType.EAGER)
+    private XpenselyStandardCategories xpenselyStandardCategories;
+
+    @OneToMany(mappedBy = "expenseList", cascade = CascadeType.ALL, orphanRemoval = true)
+    @JsonManagedReference
+    @jakarta.persistence.OrderBy("name ASC")
+    private List<XpenselyCustomCategory> customCategories;
+
     @OneToMany(mappedBy = "expenseList", cascade = CascadeType.ALL, orphanRemoval = true)
     @JsonManagedReference
     @jakarta.persistence.OrderBy("date ASC, id ASC")

src/main/java/de/zendric/app/xpensely_server/model/InviteRequest.java

@@ -1,5 +1,7 @@
 package de.zendric.app.xpensely_server.model;
 
+import jakarta.validation.constraints.NotBlank;
+import jakarta.validation.constraints.Size;
 import lombok.AllArgsConstructor;
 import lombok.Data;
 import lombok.NoArgsConstructor;
@@ -8,6 +10,8 @@ import lombok.NoArgsConstructor;
 @AllArgsConstructor
 @NoArgsConstructor
 public class InviteRequest {
+
+    @NotBlank(message = "Invite code is required")
+    @Size(min = 6, max = 6, message = "Invite code must be exactly 6 characters")
     private String inviteCode;
-    private Long userId;
 }

src/main/java/de/zendric/app/xpensely_server/model/XpenselyCustomCategory.java

@@ -0,0 +1,37 @@
+package de.zendric.app.xpensely_server.model;
+
+import com.fasterxml.jackson.annotation.JsonBackReference;
+
+import jakarta.persistence.Column;
+import jakarta.persistence.Entity;
+import jakarta.persistence.GeneratedValue;
+import jakarta.persistence.GenerationType;
+import jakarta.persistence.Id;
+import jakarta.persistence.JoinColumn;
+import jakarta.persistence.ManyToOne;
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+
+@Entity
+@Getter
+@Setter
+@AllArgsConstructor
+@NoArgsConstructor
+public class XpenselyCustomCategory {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    private String name;
+
+    @Column(name = "color_code", length = 7, nullable = false)
+    private String colorCode;
+
+    @ManyToOne
+    @JoinColumn(name = "expense_list_id", nullable = false)
+    @JsonBackReference
+    private ExpenseList expenseList;
+}

src/main/java/de/zendric/app/xpensely_server/model/XpenselyStandardCategories.java

@@ -0,0 +1,29 @@
+package de.zendric.app.xpensely_server.model;
+
+import java.util.List;
+
+import jakarta.persistence.CascadeType;
+import jakarta.persistence.Entity;
+import jakarta.persistence.FetchType;
+import jakarta.persistence.Id;
+import jakarta.persistence.JoinColumn;
+import jakarta.persistence.OneToMany;
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+
+@Entity
+@Getter
+@Setter
+@AllArgsConstructor
+@NoArgsConstructor
+public class XpenselyStandardCategories {
+
+    @Id
+    private Long id;
+
+    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER, orphanRemoval = true)
+    @JoinColumn(name = "global_categories_id")
+    private List<XpenselyStandardCategory> categories;
+}

src/main/java/de/zendric/app/xpensely_server/model/XpenselyStandardCategory.java

@@ -0,0 +1,27 @@
+package de.zendric.app.xpensely_server.model;
+
+import jakarta.persistence.Column;
+import jakarta.persistence.Entity;
+import jakarta.persistence.GeneratedValue;
+import jakarta.persistence.GenerationType;
+import jakarta.persistence.Id;
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+
+@Entity
+@Getter
+@Setter
+@AllArgsConstructor
+@NoArgsConstructor
+public class XpenselyStandardCategory {
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    private String name;
+
+    @Column(name = "color_code", length = 7, nullable = false)
+    private String colorCode;
+}

src/main/java/de/zendric/app/xpensely_server/preparation/DataInitializer.java

@@ -0,0 +1,40 @@
+package de.zendric.app.xpensely_server.preparation;
+
+import java.util.List;
+import java.util.Optional;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.CommandLineRunner;
+import org.springframework.stereotype.Component;
+
+import de.zendric.app.xpensely_server.model.XpenselyStandardCategories;
+import de.zendric.app.xpensely_server.model.XpenselyStandardCategory;
+import de.zendric.app.xpensely_server.repo.XpenselyStandardCategoriesRepository;
+
+@Component
+public class DataInitializer implements CommandLineRunner {
+
+    @Autowired
+    private XpenselyStandardCategoriesRepository globalRepo;
+
+    @Override
+    public void run(String... args) throws Exception {
+        Optional<XpenselyStandardCategories> optional = globalRepo.findById(1L);
+
+        XpenselyStandardCategories global = optional.orElseGet(() -> {
+            XpenselyStandardCategories g = new XpenselyStandardCategories();
+            g.setId(1L);
+            return g;
+        });
+
+        List<XpenselyStandardCategory> categories = List.of(
+                new XpenselyStandardCategory(null, "Food", "#FF5733"),
+                new XpenselyStandardCategory(null, "Transportation", "#33C3FF"),
+                new XpenselyStandardCategory(null, "Entertainment", "#33FF57"),
+                new XpenselyStandardCategory(null, "Shopping", "#FF33A8"),
+                new XpenselyStandardCategory(null, "Household", "#FFC733"),
+                new XpenselyStandardCategory(null, "Other", "#9D33FF"));
+        global.setCategories(categories);
+        globalRepo.save(global);
+    }
+}

src/main/java/de/zendric/app/xpensely_server/repo/ExpenseListRepository.java

@@ -3,13 +3,22 @@ package de.zendric.app.xpensely_server.repo;
 import java.util.List;
 
 import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Query;
+import org.springframework.data.repository.query.Param;
 import org.springframework.stereotype.Repository;
 
 import de.zendric.app.xpensely_server.model.ExpenseList;
 
 @Repository
 public interface ExpenseListRepository extends JpaRepository<ExpenseList, Long> {
+
     List<ExpenseList> findByOwnerId(Long ownerId);
 
     ExpenseList findByInviteCode(String inviteCode);
-}
+
+    @Query("SELECT el FROM ExpenseList el WHERE el.owner.id = :userId OR el.sharedWith.id = :userId")
+    List<ExpenseList> findByOwnerIdOrSharedWithId(@Param("userId") Long userId);
+
+    @Query("SELECT el FROM ExpenseList el WHERE el.owner.username = :username OR el.sharedWith.username = :username")
+    List<ExpenseList> findByOwnerUsernameOrSharedWithUsername(@Param("username") String username);
+}

src/main/java/de/zendric/app/xpensely_server/repo/XpenselyCustomCategoryRepository.java

@@ -0,0 +1,10 @@
+package de.zendric.app.xpensely_server.repo;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Repository;
+
+import de.zendric.app.xpensely_server.model.XpenselyCustomCategory;
+
+@Repository
+public interface XpenselyCustomCategoryRepository extends JpaRepository<XpenselyCustomCategory, Long> {
+}

src/main/java/de/zendric/app/xpensely_server/repo/XpenselyStandardCategoriesRepository.java

@@ -0,0 +1,11 @@
+package de.zendric.app.xpensely_server.repo;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Repository;
+
+import de.zendric.app.xpensely_server.model.XpenselyStandardCategories;
+
+@Repository
+public interface XpenselyStandardCategoriesRepository extends JpaRepository<XpenselyStandardCategories, Long> {
+
+}

src/main/java/de/zendric/app/xpensely_server/security/AuthenticatedUserResolver.java

@@ -0,0 +1,36 @@
+package de.zendric.app.xpensely_server.security;
+
+import de.zendric.app.xpensely_server.model.AppUser;
+import de.zendric.app.xpensely_server.services.UserService;
+import org.springframework.http.HttpStatus;
+import org.springframework.security.core.Authentication;
+import org.springframework.security.oauth2.jwt.Jwt;
+import org.springframework.stereotype.Component;
+import org.springframework.web.server.ResponseStatusException;
+
+@Component
+public class AuthenticatedUserResolver {
+
+    private final UserService userService;
+
+    public AuthenticatedUserResolver(UserService userService) {
+        this.userService = userService;
+    }
+
+    public AppUser resolveCurrentUser(Authentication authentication) {
+        if (authentication == null) {
+            throw new ResponseStatusException(HttpStatus.FORBIDDEN, "Not authenticated");
+        }
+        Jwt jwt = (Jwt) authentication.getPrincipal();
+        String googleId = jwt.getSubject();
+        try {
+            AppUser user = userService.getUserByGoogleId(googleId);
+            if (user == null) {
+                throw new ResponseStatusException(HttpStatus.FORBIDDEN, "User not registered");
+            }
+            return user;
+        } catch (IllegalArgumentException e) {
+            throw new ResponseStatusException(HttpStatus.FORBIDDEN, "User not registered");
+        }
+    }
+}

src/main/java/de/zendric/app/xpensely_server/security/RateLimitFilter.java

@@ -0,0 +1,61 @@
+package de.zendric.app.xpensely_server.security;
+
+import io.github.bucket4j.Bandwidth;
+import io.github.bucket4j.Bucket;
+import jakarta.servlet.FilterChain;
+import jakarta.servlet.ServletException;
+import jakarta.servlet.http.HttpServletRequest;
+import jakarta.servlet.http.HttpServletResponse;
+import org.springframework.http.HttpStatus;
+import org.springframework.security.core.Authentication;
+import org.springframework.security.core.context.SecurityContextHolder;
+import org.springframework.security.oauth2.jwt.Jwt;
+import org.springframework.web.filter.OncePerRequestFilter;
+
+import java.io.IOException;
+import java.time.Duration;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+public class RateLimitFilter extends OncePerRequestFilter {
+
+    private static final int REQUESTS_PER_MINUTE = 60;
+
+    private final Map<String, Bucket> buckets = new ConcurrentHashMap<>();
+
+    @Override
+    protected void doFilterInternal(HttpServletRequest request,
+                                    HttpServletResponse response,
+                                    FilterChain filterChain) throws ServletException, IOException {
+        String key = resolveKey(request);
+        Bucket bucket = buckets.computeIfAbsent(key, k -> newBucket());
+
+        if (bucket.tryConsume(1)) {
+            filterChain.doFilter(request, response);
+        } else {
+            response.setStatus(HttpStatus.TOO_MANY_REQUESTS.value());
+            response.getWriter().write("Rate limit exceeded");
+        }
+    }
+
+    private String resolveKey(HttpServletRequest request) {
+        Authentication auth = SecurityContextHolder.getContext().getAuthentication();
+        if (auth != null && auth.getPrincipal() instanceof Jwt jwt) {
+            return "user:" + jwt.getSubject();
+        }
+        String ip = request.getHeader("X-Forwarded-For");
+        if (ip != null && !ip.isBlank()) {
+            return "ip:" + ip.split(",")[0].trim();
+        }
+        return "ip:" + request.getRemoteAddr();
+    }
+
+    private Bucket newBucket() {
+        return Bucket.builder()
+                .addLimit(Bandwidth.builder()
+                        .capacity(REQUESTS_PER_MINUTE)
+                        .refillGreedy(REQUESTS_PER_MINUTE, Duration.ofMinutes(1))
+                        .build())
+                .build();
+    }
+}

src/main/java/de/zendric/app/xpensely_server/security/SecurityConfig.java

@@ -2,25 +2,29 @@ package de.zendric.app.xpensely_server.security;
 
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.Profile;
 import org.springframework.security.config.Customizer;
 import org.springframework.security.config.annotation.web.builders.HttpSecurity;
 import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
+import org.springframework.security.oauth2.server.resource.web.BearerTokenAuthenticationFilter;
 import org.springframework.security.web.SecurityFilterChain;
 
 @Configuration
 @EnableWebSecurity
 public class SecurityConfig {
-        // @Bean
-        // public SecurityFilterChain securityFilterChain(HttpSecurity http) throws
-        // Exception {
-        // http.authorizeHttpRequests(auth -> auth
-        // .anyRequest().permitAll()).csrf().disable();
-        // ;
+        @Bean
+        @Profile("test") // Only enable this for testing
+        public SecurityFilterChain testSecurityFilterChain(HttpSecurity http) throws Exception {
+                http
+                                .authorizeHttpRequests(auth -> auth
+                                                .anyRequest().permitAll())
+                                .csrf().disable();
 
-        // return http.build();
-        // }
+                return http.build();
+        }
 
         @Bean
+        @Profile("!test")
         public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception {
                 http
                                 .authorizeHttpRequests(auth -> auth
@@ -28,6 +32,7 @@ public class SecurityConfig {
                                 .oauth2ResourceServer(oauth2 -> oauth2
                                                 .jwt(Customizer.withDefaults()))
                                 .oauth2Login(Customizer.withDefaults())
+                                .addFilterAfter(new RateLimitFilter(), BearerTokenAuthenticationFilter.class)
                                 .csrf().disable();
 
                 return http.build();

src/main/java/de/zendric/app/xpensely_server/services/CategoryService.java

@@ -0,0 +1,24 @@
+package de.zendric.app.xpensely_server.services;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Service;
+
+import de.zendric.app.xpensely_server.model.XpenselyStandardCategories;
+import de.zendric.app.xpensely_server.repo.XpenselyStandardCategoriesRepository;
+
+@Service
+public class CategoryService {
+
+    private final XpenselyStandardCategoriesRepository standardCategoriesRepo;
+
+    @Autowired
+    public CategoryService(XpenselyStandardCategoriesRepository standardCategoriesRepo) {
+        this.standardCategoriesRepo = standardCategoriesRepo;
+    }
+
+    public XpenselyStandardCategories getDefaultCategories() {
+        return standardCategoriesRepo.findById(1L)
+                .orElseThrow(() -> new IllegalStateException("Standard categories not found"));
+    }
+
+}

src/main/java/de/zendric/app/xpensely_server/services/ExpenseListService.java

@@ -1,37 +1,34 @@
 package de.zendric.app.xpensely_server.services;
 
 import java.time.LocalDateTime;
-import java.util.ArrayList;
-import java.util.HashSet;
 import java.util.List;
 import java.util.Optional;
 import java.util.UUID;
 
-import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
-import de.zendric.app.xpensely_server.model.AppUser;
 import de.zendric.app.xpensely_server.model.Expense;
 import de.zendric.app.xpensely_server.model.ExpenseList;
+import de.zendric.app.xpensely_server.model.Exception.ResourceNotFoundException;
+import de.zendric.app.xpensely_server.model.XpenselyCustomCategory;
 import de.zendric.app.xpensely_server.repo.ExpenseListRepository;
 import de.zendric.app.xpensely_server.repo.ExpenseRepository;
-import jakarta.persistence.EntityManager;
+import de.zendric.app.xpensely_server.repo.XpenselyCustomCategoryRepository;
 
 @Service
 @Transactional
 public class ExpenseListService {
 
-    private ExpenseListRepository repository;
+    private final ExpenseListRepository repository;
     private final ExpenseRepository expenseRepository;
+    private final XpenselyCustomCategoryRepository customCategoryRepository;
 
-    @Autowired
-    private EntityManager entityManager;
-
-    @Autowired
-    public ExpenseListService(ExpenseListRepository repository, ExpenseRepository expenseRepository) {
+    public ExpenseListService(ExpenseListRepository repository, ExpenseRepository expenseRepository,
+            XpenselyCustomCategoryRepository customCategoryRepository) {
         this.repository = repository;
         this.expenseRepository = expenseRepository;
+        this.customCategoryRepository = customCategoryRepository;
     }
 
     public List<ExpenseList> getAllLists() {
@@ -63,67 +60,24 @@ public class ExpenseListService {
     }
 
     public List<ExpenseList> findByUserId(Long id) {
-        List<ExpenseList> allLists = repository.findAll();
-        List<ExpenseList> userSpecificList = new ArrayList<>();
-        for (ExpenseList expenseList : allLists) {
-            AppUser sharedWith = expenseList.getSharedWith();
-
-            if (expenseList.getOwner().getId().equals(id)) {
-                userSpecificList.add(expenseList);
-            } else {
-                if (sharedWith != null && sharedWith.getId().equals(id)) {
-                    userSpecificList.add(expenseList);
-                }
-            }
-        }
-        return userSpecificList;
+        return repository.findByOwnerIdOrSharedWithId(id);
     }
 
     public List<ExpenseList> findByUsername(String username) {
-        List<ExpenseList> allLists = repository.findAll();
-        List<ExpenseList> userSpecificList = new ArrayList<>();
-        for (ExpenseList expenseList : allLists) {
-            AppUser sharedWith = expenseList.getSharedWith();
-
-            if (expenseList.getOwner().getUsername().equals(username)) {
-                userSpecificList.add(expenseList);
-            } else {
-                if (sharedWith != null && sharedWith.getUsername().equals(username)) {
-                    userSpecificList.add(expenseList);
-                }
-            }
-        }
-        return userSpecificList;
-
+        return repository.findByOwnerUsernameOrSharedWithUsername(username);
     }
 
     public Expense addExpenseToList(Long expenseListId, Expense expense) {
-        // find expenseList
         ExpenseList expenseList = repository.findById(expenseListId)
-                .orElseThrow(() -> new RuntimeException("ExpenseList not found with id: " + expenseListId));
-        // get all added expenses
-        HashSet<Long> existingId = new HashSet<>();
-        for (Expense e : expenseList.getExpenses()) {
-            existingId.add(e.getId());
-        }
-        // add the new expense
+                .orElseThrow(() -> new ResourceNotFoundException("ExpenseList not found with id: " + expenseListId));
         expenseList.addExpense(expense);
-        // save
         repository.save(expenseList);
-
-        Expense newExpense = new Expense();
-        for (Expense e : expenseList.getExpenses()) {
-            if (!existingId.contains(e.getId())) {
-                newExpense = e;
-                break;
-            }
-        }
-        return newExpense;
+        return expense;
     }
 
     public void deleteExpenseFromList(Long expenseListId, Long expenseId) {
         ExpenseList expenseList = repository.findById(expenseListId)
-                .orElseThrow(() -> new RuntimeException("ExpenseList not found with id: " + expenseListId));
+                .orElseThrow(() -> new ResourceNotFoundException("ExpenseList not found with id: " + expenseListId));
         Expense expenseToRemove = null;
         for (Expense expense : expenseList.getExpenses()) {
             if (expense.getId().equals(expenseId)) {
@@ -134,14 +88,14 @@ public class ExpenseListService {
         if (expenseToRemove != null) {
             expenseList.removeExpense(expenseToRemove);
         } else {
-            throw new RuntimeException("Expense not found with id: " + expenseId);
+            throw new ResourceNotFoundException("Expense not found with id: " + expenseId);
         }
         repository.save(expenseList);
     }
 
     public String generateInviteCode(Long listId) {
         ExpenseList list = repository.findById(listId)
-                .orElseThrow(() -> new RuntimeException("List not found"));
+                .orElseThrow(() -> new ResourceNotFoundException("List not found"));
         String inviteCode;
         if (list.getInviteCode() == null || list.getInviteCodeExpiration().isBefore(LocalDateTime.now())) {
 
@@ -163,7 +117,7 @@ public class ExpenseListService {
 
     public Expense updateExpense(Long expenseListId, Expense updatedExpense) {
         ExpenseList expenseList = repository.findById(expenseListId)
-                .orElseThrow(() -> new IllegalArgumentException("ExpenseList not found"));
+                .orElseThrow(() -> new ResourceNotFoundException("ExpenseList not found with id: " + expenseListId));
 
         if (!expenseList.getExpenses().stream()
                 .anyMatch(expense -> expense.getId().equals(updatedExpense.getId()))) {
@@ -171,14 +125,35 @@ public class ExpenseListService {
         }
 
         Expense existingExpense = expenseRepository.findById(updatedExpense.getId())
-                .orElseThrow(() -> new IllegalArgumentException("Expense not found"));
+                .orElseThrow(() -> new ResourceNotFoundException("Expense not found with id: " + updatedExpense.getId()));
         existingExpense.setTitle(updatedExpense.getTitle());
         existingExpense.setAmount(updatedExpense.getAmount());
         existingExpense.setPersonalUseAmount(updatedExpense.getPersonalUseAmount());
         existingExpense.setOtherPersonAmount(updatedExpense.getOtherPersonAmount());
         existingExpense.setDate(updatedExpense.getDate());
         existingExpense.setOwner(updatedExpense.getOwner());
+        existingExpense.setCategory(updatedExpense.getCategory());
 
         return expenseRepository.save(existingExpense);
     }
+
+    // TODO implement API for this
+    public XpenselyCustomCategory addCustomCategory(Long expenseListId, XpenselyCustomCategory customCategory) {
+        ExpenseList expenseList = repository.findById(expenseListId)
+                .orElseThrow(() -> new ResourceNotFoundException("Expense List not found"));
+        customCategory.setExpenseList(expenseList);
+
+        return customCategoryRepository.save(customCategory);
+    }
+
+    // TODO implement API for this
+    public void deleteCustomCategory(Long expenseListId, Long categoryId) {
+        XpenselyCustomCategory category = customCategoryRepository.findById(categoryId)
+                .orElseThrow(() -> new ResourceNotFoundException("Custom Category not found"));
+        if (!category.getExpenseList().getId().equals(expenseListId)) {
+            throw new IllegalArgumentException("Category does not belong to the specified Expense List");
+        }
+        customCategoryRepository.delete(category);
+    }
+
 }

src/main/java/de/zendric/app/xpensely_server/services/UserService.java

@@ -1,12 +1,12 @@
 package de.zendric.app.xpensely_server.services;
 
 import java.util.List;
-import java.util.Optional;
 
 import org.springframework.stereotype.Service;
 
 import de.zendric.app.xpensely_server.model.AppUser;
-import de.zendric.app.xpensely_server.model.UsernameAlreadyExistsException;
+import de.zendric.app.xpensely_server.model.Exception.ResourceNotFoundException;
+import de.zendric.app.xpensely_server.model.Exception.UsernameAlreadyExistsException;
 import de.zendric.app.xpensely_server.repo.UserRepository;
 
 @Service
@@ -29,36 +29,24 @@ public class UserService {
     }
 
     public AppUser getUser(Long id) {
-        Optional<AppUser> user = userRepository.findById(id);
-        if (user.isPresent()) {
-            return user.get();
-        } else
-            return null;
+        return userRepository.findById(id)
+                .orElseThrow(() -> new ResourceNotFoundException("User not found with id: " + id));
     }
 
     public AppUser deleteUserById(Long id) {
-        Optional<AppUser> user = userRepository.findById(id);
-        if (user.isPresent()) {
-            userRepository.deleteById(id);
-            return user.get();
-        } else
-            return null;
+        AppUser user = userRepository.findById(id)
+                .orElseThrow(() -> new ResourceNotFoundException("User not found with id: " + id));
+        userRepository.deleteById(id);
+        return user;
     }
 
     public AppUser getUserByName(String username) {
-        Optional<AppUser> optUser = userRepository.findByUsername(username);
-        if (optUser.isPresent()) {
-            return optUser.get();
-        } else
-            return null;
+        return userRepository.findByUsername(username)
+                .orElseThrow(() -> new ResourceNotFoundException("User not found: " + username));
     }
 
     public AppUser getUserByGoogleId(String id) {
-        Optional<AppUser> optUser = userRepository.findByGoogleId(id);
-        if (optUser.isPresent()) {
-            return optUser.get();
-        } else
-            return null;
+        return userRepository.findByGoogleId(id)
+                .orElseThrow(() -> new ResourceNotFoundException("User not found with Google ID: " + id));
     }
-
-}
+}

src/test/java/de/zendric/app/xpensely_Server/ExpenseListRepositoryTest.java

@@ -0,0 +1,47 @@
+package de.zendric.app.xpensely_Server;
+
+import de.zendric.app.xpensely_server.model.ExpenseList;
+import de.zendric.app.xpensely_server.repo.ExpenseListRepository;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;
+
+import java.util.Optional;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+@DataJpaTest
+class ExpenseListRepositoryTest {
+
+    @Autowired
+    private ExpenseListRepository expenseListRepository;
+
+    @Test
+    void saveAndFindById_returnsExpenseList() {
+        ExpenseList list = new ExpenseList();
+        list.setName("Groceries");
+        ExpenseList saved = expenseListRepository.save(list);
+
+        Optional<ExpenseList> found = expenseListRepository.findById(saved.getId());
+
+        assertTrue(found.isPresent());
+        assertEquals("Groceries", found.get().getName());
+    }
+
+    @Test
+    void findById_nonExistentId_returnsEmpty() {
+        Optional<ExpenseList> found = expenseListRepository.findById(999L);
+        assertTrue(found.isEmpty());
+    }
+
+    @Test
+    void delete_removesFromRepository() {
+        ExpenseList list = new ExpenseList();
+        list.setName("To Delete");
+        ExpenseList saved = expenseListRepository.save(list);
+
+        expenseListRepository.deleteById(saved.getId());
+
+        assertTrue(expenseListRepository.findById(saved.getId()).isEmpty());
+    }
+}

src/test/java/de/zendric/app/xpensely_Server/XpenselyServerApplicationTests.java

@@ -1,13 +0,0 @@
-package de.zendric.app.xpensely_Server;
-
-import org.junit.jupiter.api.Test;
-import org.springframework.boot.test.context.SpringBootTest;
-
-@SpringBootTest
-class XpenselyServerApplicationTests {
-
-	@Test
-	void contextLoads() {
-	}
-
-}

src/test/java/de/zendric/app/xpensely_Server/controller/AppUserControllerTest.java

@@ -0,0 +1,95 @@
+package de.zendric.app.xpensely_Server.controller;
+
+import de.zendric.app.xpensely_server.controller.AppUserController;
+import de.zendric.app.xpensely_server.model.AppUser;
+import de.zendric.app.xpensely_server.security.AuthenticatedUserResolver;
+import de.zendric.app.xpensely_server.services.UserService;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
+import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
+import org.springframework.http.MediaType;
+import org.springframework.test.context.ActiveProfiles;
+import org.springframework.test.context.bean.override.mockito.MockitoBean;
+import org.springframework.test.web.servlet.MockMvc;
+
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.when;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.*;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;
+
+@WebMvcTest(AppUserController.class)
+@AutoConfigureMockMvc(addFilters = false)
+@ActiveProfiles("test")
+class AppUserControllerTest {
+
+    @Autowired MockMvc mockMvc;
+    @MockitoBean UserService userService;
+    @MockitoBean AuthenticatedUserResolver authenticatedUserResolver;
+
+    @Test
+    void createUser_blankUsername_returns400WithFieldError() throws Exception {
+        mockMvc.perform(post("/api/users/createUser")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"username\":\"\",\"googleId\":\"gid123\"}"))
+                .andExpect(status().isBadRequest())
+                .andExpect(jsonPath("$.username").exists());
+    }
+
+    @Test
+    void createUser_invalidUsernamePattern_returns400() throws Exception {
+        mockMvc.perform(post("/api/users/createUser")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"username\":\"hello world!\",\"googleId\":\"gid123\"}"))
+                .andExpect(status().isBadRequest())
+                .andExpect(jsonPath("$.username").exists());
+    }
+
+    @Test
+    void createUser_usernameTooShort_returns400() throws Exception {
+        mockMvc.perform(post("/api/users/createUser")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"username\":\"ab\",\"googleId\":\"gid123\"}"))
+                .andExpect(status().isBadRequest())
+                .andExpect(jsonPath("$.username").exists());
+    }
+
+    @Test
+    void createUser_blankGoogleId_returns400() throws Exception {
+        mockMvc.perform(post("/api/users/createUser")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"username\":\"validuser\",\"googleId\":\"\"}"))
+                .andExpect(status().isBadRequest())
+                .andExpect(jsonPath("$.googleId").exists());
+    }
+
+    // --- Authorization tests ---
+
+    @Test
+    void getUser_differentUser_returns403() throws Exception {
+        AppUser self = new AppUser(); self.setId(1L);
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(self);
+
+        mockMvc.perform(get("/api/users").param("id", "99"))
+                .andExpect(status().isForbidden());
+    }
+
+    @Test
+    void getUser_sameUser_returns200() throws Exception {
+        AppUser self = new AppUser(); self.setId(1L);
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(self);
+        when(userService.getUser(1L)).thenReturn(self);
+
+        mockMvc.perform(get("/api/users").param("id", "1"))
+                .andExpect(status().isOk());
+    }
+
+    @Test
+    void deleteUser_differentUser_returns403() throws Exception {
+        AppUser self = new AppUser(); self.setId(1L);
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(self);
+
+        mockMvc.perform(delete("/api/users").param("id", "99"))
+                .andExpect(status().isForbidden());
+    }
+}

src/test/java/de/zendric/app/xpensely_Server/controller/ExpenseListControllerTest.java

@@ -0,0 +1,135 @@
+package de.zendric.app.xpensely_Server.controller;
+
+import de.zendric.app.xpensely_server.controller.ExpenseListController;
+import de.zendric.app.xpensely_server.model.AppUser;
+import de.zendric.app.xpensely_server.model.ExpenseList;
+import de.zendric.app.xpensely_server.security.AuthenticatedUserResolver;
+import de.zendric.app.xpensely_server.services.CategoryService;
+import de.zendric.app.xpensely_server.services.ExpenseListService;
+import de.zendric.app.xpensely_server.services.UserService;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
+import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
+import org.springframework.http.MediaType;
+import org.springframework.test.context.ActiveProfiles;
+import org.springframework.test.context.bean.override.mockito.MockitoBean;
+import org.springframework.test.web.servlet.MockMvc;
+
+import java.util.List;
+import java.util.Optional;
+
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.when;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.*;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;
+
+@WebMvcTest(ExpenseListController.class)
+@AutoConfigureMockMvc(addFilters = false)
+@ActiveProfiles("test")
+class ExpenseListControllerTest {
+
+    @Autowired MockMvc mockMvc;
+    @MockitoBean ExpenseListService expenseListService;
+    @MockitoBean UserService userService;
+    @MockitoBean CategoryService categoryService;
+    @MockitoBean AuthenticatedUserResolver authenticatedUserResolver;
+
+    // --- Validation tests ---
+
+    @Test
+    void addExpense_blankTitle_returns400() throws Exception {
+        mockMvc.perform(post("/api/expenselist/1/add")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"title\":\"\",\"owner\":\"alice\",\"amount\":10.0,\"date\":\"2026-05-04\",\"category\":\"Food\"}"))
+                .andExpect(status().isBadRequest())
+                .andExpect(jsonPath("$.title").exists());
+    }
+
+    @Test
+    void addExpense_negativeAmount_returns400() throws Exception {
+        mockMvc.perform(post("/api/expenselist/1/add")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"title\":\"Lunch\",\"owner\":\"alice\",\"amount\":-5.0,\"date\":\"2026-05-04\",\"category\":\"Food\"}"))
+                .andExpect(status().isBadRequest())
+                .andExpect(jsonPath("$.amount").exists());
+    }
+
+    @Test
+    void addExpense_nullDate_returns400() throws Exception {
+        mockMvc.perform(post("/api/expenselist/1/add")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"title\":\"Lunch\",\"owner\":\"alice\",\"amount\":10.0,\"category\":\"Food\"}"))
+                .andExpect(status().isBadRequest())
+                .andExpect(jsonPath("$.date").exists());
+    }
+
+    @Test
+    void acceptInvite_blankCode_returns400() throws Exception {
+        mockMvc.perform(post("/api/expenselist/accept-invite")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"inviteCode\":\"\"}"))
+                .andExpect(status().isBadRequest())
+                .andExpect(jsonPath("$.inviteCode").exists());
+    }
+
+    @Test
+    void acceptInvite_wrongCodeLength_returns400() throws Exception {
+        mockMvc.perform(post("/api/expenselist/accept-invite")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"inviteCode\":\"ABC\"}"))
+                .andExpect(status().isBadRequest())
+                .andExpect(jsonPath("$.inviteCode").exists());
+    }
+
+    // --- Authorization tests ---
+
+    @Test
+    void getById_authenticatedUserNotMember_returns403() throws Exception {
+        AppUser owner = new AppUser(); owner.setId(1L);
+        AppUser requester = new AppUser(); requester.setId(2L);
+        ExpenseList list = new ExpenseList(); list.setId(1L); list.setOwner(owner);
+
+        when(expenseListService.findById(1L)).thenReturn(Optional.of(list));
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(requester);
+
+        mockMvc.perform(get("/api/expenselist/byId").param("id", "1"))
+                .andExpect(status().isForbidden());
+    }
+
+    @Test
+    void getById_authenticatedUserIsOwner_returns200() throws Exception {
+        AppUser owner = new AppUser(); owner.setId(1L);
+        ExpenseList list = new ExpenseList(); list.setId(1L); list.setOwner(owner);
+
+        when(expenseListService.findById(1L)).thenReturn(Optional.of(list));
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(owner);
+
+        mockMvc.perform(get("/api/expenselist/byId").param("id", "1"))
+                .andExpect(status().isOk());
+    }
+
+    @Test
+    void deleteList_nonOwner_returns403() throws Exception {
+        AppUser owner = new AppUser(); owner.setId(1L);
+        AppUser nonOwner = new AppUser(); nonOwner.setId(2L);
+        ExpenseList list = new ExpenseList(); list.setId(5L); list.setOwner(owner);
+
+        when(expenseListService.findById(5L)).thenReturn(Optional.of(list));
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(nonOwner);
+
+        mockMvc.perform(delete("/api/expenselist/5"))
+                .andExpect(status().isForbidden());
+    }
+
+    @Test
+    void getMine_returnsCurrentUserLists() throws Exception {
+        AppUser user = new AppUser(); user.setId(3L);
+
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(user);
+        when(expenseListService.findByUserId(3L)).thenReturn(List.of(new ExpenseList()));
+
+        mockMvc.perform(get("/api/expenselist/mine"))
+                .andExpect(status().isOk());
+    }
+}

src/test/java/de/zendric/app/xpensely_Server/security/AuthenticatedUserResolverTest.java

@@ -0,0 +1,78 @@
+package de.zendric.app.xpensely_Server.security;
+
+import de.zendric.app.xpensely_server.model.AppUser;
+import de.zendric.app.xpensely_server.security.AuthenticatedUserResolver;
+import de.zendric.app.xpensely_server.services.UserService;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.http.HttpStatus;
+import org.springframework.security.oauth2.jwt.Jwt;
+import org.springframework.security.oauth2.server.resource.authentication.JwtAuthenticationToken;
+import org.springframework.web.server.ResponseStatusException;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static org.mockito.Mockito.*;
+
+class AuthenticatedUserResolverTest {
+
+    UserService userService;
+    AuthenticatedUserResolver resolver;
+
+    @BeforeEach
+    void setUp() {
+        userService = mock(UserService.class);
+        resolver = new AuthenticatedUserResolver(userService);
+    }
+
+    @Test
+    void resolveCurrentUser_validJwt_returnsAppUser() {
+        Jwt jwt = Jwt.withTokenValue("token")
+                .header("alg", "RS256")
+                .subject("google-id-123")
+                .build();
+        JwtAuthenticationToken auth = new JwtAuthenticationToken(jwt);
+
+        AppUser user = new AppUser();
+        user.setId(1L);
+        user.setGoogleId("google-id-123");
+        when(userService.getUserByGoogleId("google-id-123")).thenReturn(user);
+
+        AppUser result = resolver.resolveCurrentUser(auth);
+        assertEquals(user, result);
+    }
+
+    @Test
+    void resolveCurrentUser_userNotFound_throws403() {
+        Jwt jwt = Jwt.withTokenValue("token")
+                .header("alg", "RS256")
+                .subject("unknown-id")
+                .build();
+        JwtAuthenticationToken auth = new JwtAuthenticationToken(jwt);
+        when(userService.getUserByGoogleId("unknown-id")).thenReturn(null);
+
+        ResponseStatusException ex = assertThrows(ResponseStatusException.class,
+                () -> resolver.resolveCurrentUser(auth));
+        assertEquals(HttpStatus.FORBIDDEN, ex.getStatusCode());
+    }
+
+    @Test
+    void resolveCurrentUser_userServiceThrows_throws403() {
+        Jwt jwt = Jwt.withTokenValue("token")
+                .header("alg", "RS256")
+                .subject("gone-id")
+                .build();
+        JwtAuthenticationToken auth = new JwtAuthenticationToken(jwt);
+        when(userService.getUserByGoogleId("gone-id")).thenThrow(new IllegalArgumentException("not found"));
+
+        ResponseStatusException ex = assertThrows(ResponseStatusException.class,
+                () -> resolver.resolveCurrentUser(auth));
+        assertEquals(HttpStatus.FORBIDDEN, ex.getStatusCode());
+    }
+
+    @Test
+    void resolveCurrentUser_nullAuthentication_throws403() {
+        ResponseStatusException ex = assertThrows(ResponseStatusException.class,
+                () -> resolver.resolveCurrentUser(null));
+        assertEquals(HttpStatus.FORBIDDEN, ex.getStatusCode());
+    }
+}

src/test/java/de/zendric/app/xpensely_Server/security/RateLimitFilterTest.java

@@ -0,0 +1,89 @@
+package de.zendric.app.xpensely_Server.security;
+
+import de.zendric.app.xpensely_server.security.RateLimitFilter;
+import jakarta.servlet.FilterChain;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.mock.web.MockHttpServletRequest;
+import org.springframework.mock.web.MockHttpServletResponse;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.mockito.Mockito.*;
+
+class RateLimitFilterTest {
+
+    RateLimitFilter filter;
+    FilterChain chain;
+
+    @BeforeEach
+    void setUp() {
+        filter = new RateLimitFilter();
+        chain = mock(FilterChain.class);
+    }
+
+    @Test
+    void allowsRequestUnderLimit() throws Exception {
+        MockHttpServletRequest request = new MockHttpServletRequest();
+        request.setRemoteAddr("1.2.3.4");
+        MockHttpServletResponse response = new MockHttpServletResponse();
+
+        filter.doFilter(request, response, chain);
+
+        verify(chain, times(1)).doFilter(request, response);
+        assertEquals(200, response.getStatus());
+    }
+
+    @Test
+    void blocksRequestOverLimit() throws Exception {
+        MockHttpServletRequest request = new MockHttpServletRequest();
+        request.setRemoteAddr("5.6.7.8");
+
+        for (int i = 0; i < 60; i++) {
+            filter.doFilter(request, new MockHttpServletResponse(), chain);
+        }
+
+        MockHttpServletResponse blockedResponse = new MockHttpServletResponse();
+        filter.doFilter(request, blockedResponse, chain);
+
+        assertEquals(429, blockedResponse.getStatus());
+        verify(chain, times(60)).doFilter(eq(request), any());
+    }
+
+    @Test
+    void differentIpsBucketedSeparately() throws Exception {
+        MockHttpServletRequest req1 = new MockHttpServletRequest();
+        req1.setRemoteAddr("10.0.0.1");
+        MockHttpServletRequest req2 = new MockHttpServletRequest();
+        req2.setRemoteAddr("10.0.0.2");
+
+        for (int i = 0; i < 60; i++) {
+            filter.doFilter(req1, new MockHttpServletResponse(), chain);
+        }
+
+        MockHttpServletResponse response2 = new MockHttpServletResponse();
+        filter.doFilter(req2, response2, chain);
+
+        assertEquals(200, response2.getStatus());
+    }
+
+    @Test
+    void prefersXForwardedForHeader() throws Exception {
+        MockHttpServletRequest request = new MockHttpServletRequest();
+        request.setRemoteAddr("192.168.1.1");
+        request.addHeader("X-Forwarded-For", "203.0.113.5, 10.0.0.1");
+
+        for (int i = 0; i < 60; i++) {
+            filter.doFilter(request, new MockHttpServletResponse(), chain);
+        }
+
+        MockHttpServletResponse blocked = new MockHttpServletResponse();
+        filter.doFilter(request, blocked, chain);
+        assertEquals(429, blocked.getStatus());
+
+        MockHttpServletRequest directRequest = new MockHttpServletRequest();
+        directRequest.setRemoteAddr("192.168.1.1");
+        MockHttpServletResponse directResponse = new MockHttpServletResponse();
+        filter.doFilter(directRequest, directResponse, chain);
+        assertEquals(200, directResponse.getStatus());
+    }
+}

src/test/java/de/zendric/app/xpensely_Server/services/ExpenseListServiceTest.java

@@ -0,0 +1,57 @@
+package de.zendric.app.xpensely_Server.services;
+
+import de.zendric.app.xpensely_server.model.AppUser;
+import de.zendric.app.xpensely_server.model.ExpenseList;
+import de.zendric.app.xpensely_server.repo.ExpenseListRepository;
+import de.zendric.app.xpensely_server.repo.ExpenseRepository;
+import de.zendric.app.xpensely_server.repo.XpenselyCustomCategoryRepository;
+import de.zendric.app.xpensely_server.services.ExpenseListService;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.InjectMocks;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+import static org.mockito.Mockito.never;
+
+@ExtendWith(MockitoExtension.class)
+class ExpenseListServiceTest {
+
+    @Mock ExpenseListRepository repository;
+    @Mock ExpenseRepository expenseRepository;
+    @Mock XpenselyCustomCategoryRepository customCategoryRepository;
+
+    @InjectMocks
+    ExpenseListService service;
+
+    @Test
+    void findByUserId_usesRepositoryQuery_notFindAll() {
+        AppUser owner = new AppUser(); owner.setId(1L);
+        ExpenseList list = new ExpenseList(); list.setId(10L); list.setOwner(owner);
+        when(repository.findByOwnerIdOrSharedWithId(1L)).thenReturn(List.of(list));
+
+        List<ExpenseList> result = service.findByUserId(1L);
+
+        assertThat(result).hasSize(1);
+        verify(repository).findByOwnerIdOrSharedWithId(1L);
+        verify(repository, never()).findAll();
+    }
+
+    @Test
+    void findByUsername_usesRepositoryQuery_notFindAll() {
+        AppUser owner = new AppUser(); owner.setId(1L); owner.setUsername("alice");
+        ExpenseList list = new ExpenseList(); list.setId(10L); list.setOwner(owner);
+        when(repository.findByOwnerUsernameOrSharedWithUsername("alice")).thenReturn(List.of(list));
+
+        List<ExpenseList> result = service.findByUsername("alice");
+
+        assertThat(result).hasSize(1);
+        verify(repository).findByOwnerUsernameOrSharedWithUsername("alice");
+        verify(repository, never()).findAll();
+    }
+}

src/test/java/de/zendric/app/xpensely_Server/services/UserServiceTest.java

@@ -0,0 +1,75 @@
+package de.zendric.app.xpensely_Server.services;
+
+import de.zendric.app.xpensely_server.model.AppUser;
+import de.zendric.app.xpensely_server.model.Exception.ResourceNotFoundException;
+import de.zendric.app.xpensely_server.repo.UserRepository;
+import de.zendric.app.xpensely_server.services.UserService;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.InjectMocks;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import java.util.Optional;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.mockito.Mockito.when;
+
+@ExtendWith(MockitoExtension.class)
+class UserServiceTest {
+
+    @Mock
+    UserRepository userRepository;
+
+    @InjectMocks
+    UserService userService;
+
+    @Test
+    void getUserByName_throwsResourceNotFound_whenUserMissing() {
+        when(userRepository.findByUsername("ghost")).thenReturn(Optional.empty());
+
+        assertThatThrownBy(() -> userService.getUserByName("ghost"))
+                .isInstanceOf(ResourceNotFoundException.class)
+                .hasMessageContaining("ghost");
+    }
+
+    @Test
+    void getUserByName_returnsUser_whenFound() {
+        AppUser user = new AppUser();
+        user.setId(1L);
+        user.setUsername("alice");
+        when(userRepository.findByUsername("alice")).thenReturn(Optional.of(user));
+
+        AppUser result = userService.getUserByName("alice");
+
+        assertThat(result.getUsername()).isEqualTo("alice");
+    }
+
+    @Test
+    void getUser_throwsResourceNotFound_whenIdMissing() {
+        when(userRepository.findById(99L)).thenReturn(Optional.empty());
+
+        assertThatThrownBy(() -> userService.getUser(99L))
+                .isInstanceOf(ResourceNotFoundException.class)
+                .hasMessageContaining("99");
+    }
+
+    @Test
+    void deleteUserById_throwsResourceNotFound_whenIdMissing() {
+        when(userRepository.findById(99L)).thenReturn(Optional.empty());
+
+        assertThatThrownBy(() -> userService.deleteUserById(99L))
+                .isInstanceOf(ResourceNotFoundException.class)
+                .hasMessageContaining("99");
+    }
+
+    @Test
+    void getUserByGoogleId_throwsResourceNotFound_whenMissing() {
+        when(userRepository.findByGoogleId("gid-404")).thenReturn(Optional.empty());
+
+        assertThatThrownBy(() -> userService.getUserByGoogleId("gid-404"))
+                .isInstanceOf(ResourceNotFoundException.class)
+                .hasMessageContaining("gid-404");
+    }
+}