diff --git a/.claude/settings.local.json b/.claude/settings.local.json
new file mode 100644
index 0000000..4bb51fb
--- /dev/null
+++ b/.claude/settings.local.json
@@ -0,0 +1,8 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(git add *)",
+      "Bash(git commit *)"
+    ]
+  }
+}
diff --git a/docker-compose.yml b/docker-compose.yml
index c319a7d..64b6e0e 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -4,9 +4,6 @@ services:
     pull_policy: always
     restart: always
     environment:
-      GOOGLE_CLIENT_ID: ${GOOGLE_CLIENT_ID}
-      GOOGLE_CLIENT_SECRET: ${GOOGLE_CLIENT_SECRET}
-
       DB_PORT: 5432
       DB_P_NAME: ${POSTGRES_DB}
       DB_USERNAME: ${POSTGRES_USER}
diff --git a/docs/API.md b/docs/API.md
index 68fe07c..c4ffb65 100644
--- a/docs/API.md
+++ b/docs/API.md
@@ -1,6 +1,6 @@
 # Xpensely Server — API Reference
 
-> Last updated: 2026-05-09 · Branch: `feature/security-hardening`
+> Last updated: 2026-05-14 · Branch: `dev`
 
 ## Table of Contents
 1. [Overview](#1-overview)
@@ -28,6 +28,7 @@ Xpensely Server is a Spring Boot REST API that manages shared expense lists for
 | Method | Path | Description |
 |--------|------|-------------|
 | GET | `/` | Health check — returns `"Welcome"` |
+| GET | `/api/version` | Returns build version and timestamp |
 | POST | `/api/users/createUser` | Register a new user |
 | GET | `/api/users/byName` | Look up a user by username |
 
@@ -98,6 +99,25 @@ Welcome
 
 ---
 
+#### `GET /api/version`
+
+Returns the application version and build timestamp. No authentication required.
+
+**Response:** `200 OK`
+```json
+{
+  "version": "0.0.1-SNAPSHOT",
+  "builtAt": "2026-05-09T10:00:00Z"
+}
+```
+
+| Field | Type | Notes |
+|-------|------|-------|
+| `version` | String | Maven project version |
+| `builtAt` | String (ISO-8601) | UTC timestamp of the build |
+
+---
+
 ### 4.2 Users
 
 Base path: `/api/users`
@@ -121,7 +141,7 @@ Base path: `/api/users`
 | `username` | String | Required. 3–30 chars. Pattern: `^[a-zA-Z0-9_.\-]+$` |
 | `googleId` | String | Required. Non-blank. Must match the JWT `sub` from Google. |
 
-**Success response:** `200 OK` — returns the created [AppUser](#appuser) object.
+**Success response:** `201 Created` — returns the created [AppUser](#appuser) object.
 
 **Error responses:**
 | Status | Condition |
@@ -145,6 +165,7 @@ Base path: `/api/users`
 **Error responses:**
 | Status | Condition |
 |--------|-----------|
+| 403 | Authenticated user's ID does not match the requested `id` |
 | 404 | No user found for `id` |
 
 ---
@@ -181,6 +202,7 @@ Base path: `/api/users`
 **Error responses:**
 | Status | Condition |
 |--------|-----------|
+| 403 | Requested Google ID does not match the authenticated user's Google ID |
 | 404 | No user found for that Google ID |
 
 ---
@@ -194,11 +216,12 @@ Base path: `/api/users`
 |-------|------|----------|-------------|
 | `id` | Long | Yes | Database ID of the user to delete |
 
-**Success response:** `200 OK` — returns the deleted [AppUser](#appuser).
+**Success response:** `200 OK` — returns a plain string: `"User deleted: <username>"`.
 
 **Error responses:**
 | Status | Condition |
 |--------|-----------|
+| 403 | Authenticated user's ID does not match the requested `id` |
 | 404 | No user found for `id` |
 
 ---
@@ -219,7 +242,11 @@ Returns all expense lists where the caller is the owner **or** has been shared t
 
 **Request body:** None
 
-**Success response:** `200 OK` — array of [ExpenseList](#expenselist).
+**Success responses:**
+| Status | Condition |
+|--------|-----------|
+| 200 OK | Returns array of [ExpenseList](#expenselist) |
+| 204 No Content | Caller has no expense lists |
 
 ```json
 [
@@ -337,7 +364,7 @@ Only the **owner** may delete a list. Deleting a list cascades to all its expens
 | `date` | String (ISO-8601) | Required. Format: `YYYY-MM-DD`. |
 | `category` | String | Required. Non-blank category name. |
 
-**Success response:** `200 OK` — returns the created [Expense](#expense).
+**Success response:** `201 Created` — returns the created [Expense](#expense).
 
 **Error responses:**
 | Status | Condition |
@@ -411,7 +438,7 @@ Caller must be a member of the list. Expense must belong to the specified list.
 
 Caller must be a member of the list.
 
-**Success response:** `200 OK` — returns the deleted [Expense](#expense).
+**Success response:** `204 No Content`
 
 **Error responses:**
 | Status | Condition |
@@ -465,13 +492,14 @@ Joins the caller to a shared expense list using an invite code.
 |-------|------|-------------|
 | `inviteCode` | String | Required. Exactly 6 characters. |
 
-**Success response:** `200 OK` — returns the [ExpenseList](#expenselist) the caller joined.
+**Success response:** `200 OK` — returns a plain string: `"User added to the list"`.
 
 **Error responses:**
 | Status | Condition |
 |--------|-----------|
-| 400 | Validation failure or invite code not found / expired |
-| 403 | Caller is already the owner of this list |
+| 400 | Validation failure or caller is already the owner of the list |
+| 404 | Invite code not found or expired |
+| 226 IM Used | List already has a second member (`sharedWith` is not null) |
 
 ---
 
diff --git a/src/main/java/de/zendric/app/xpensely_server/security/SecurityConfig.java b/src/main/java/de/zendric/app/xpensely_server/security/SecurityConfig.java
index 2b85f99..97ef8b8 100644
--- a/src/main/java/de/zendric/app/xpensely_server/security/SecurityConfig.java
+++ b/src/main/java/de/zendric/app/xpensely_server/security/SecurityConfig.java
@@ -32,7 +32,6 @@ public class SecurityConfig {
                                                 .anyRequest().authenticated())
                                 .oauth2ResourceServer(oauth2 -> oauth2
                                                 .jwt(Customizer.withDefaults()))
-                                .oauth2Login(Customizer.withDefaults())
                                 .addFilterAfter(new RateLimitFilter(), BearerTokenAuthenticationFilter.class)
                                 .csrf(csrf -> csrf.disable());
 
diff --git a/src/main/resources/application.properties b/src/main/resources/application.properties
index 61116e5..ad7db8d 100644
--- a/src/main/resources/application.properties
+++ b/src/main/resources/application.properties
@@ -3,8 +3,6 @@ spring.application.name=XpenselyServer
 
 #Security
 spring.security.enabled=false
-spring.security.oauth2.client.registration.google.client-id=${GOOGLE_CLIENT_ID}
-spring.security.oauth2.client.registration.google.client-secret=${GOOGLE_CLIENT_SECRET}
 spring.security.oauth2.resourceserver.jwt.issuer-uri=https://accounts.google.com
 
 # PostgreSQL Configuration