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XpenselyServer/docs/API.md
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# Xpensely Server — API Reference
> Last updated: 2026-05-09 · Branch: `feature/security-hardening`
## Table of Contents
1. [Overview](#1-overview)
2. [Authentication](#2-authentication)
3. [Rate Limiting](#3-rate-limiting)
4. [Endpoints](#4-endpoints)
- 4.1 [Home](#41-home)
- 4.2 [Users](#42-users)
- 4.3 [Expense Lists](#43-expense-lists)
5. [Data Models](#5-data-models)
6. [Error Handling](#6-error-handling)
7. [Recent Changes — `feature/security-hardening`](#7-recent-changes)
---
## 1. Overview
Xpensely Server is a Spring Boot REST API that manages shared expense lists for pairs of users. It uses Google OAuth2 JWT tokens for authentication. All protected endpoints require a valid Bearer token in the `Authorization` header.
**Base URL (local dev):** `http://localhost:8080`
**Content-Type:** `application/json` for all request and response bodies.
**Public endpoints (no auth required):**
| Method | Path | Description |
|--------|------|-------------|
| GET | `/` | Health check — returns `"Welcome"` |
| POST | `/api/users/createUser` | Register a new user |
| GET | `/api/users/byName` | Look up a user by username |
All other endpoints require authentication (see [Section 2](#2-authentication)).
## 2. Authentication
The server uses **OAuth2 Resource Server** authentication with **Google ID JWT tokens**.
### How it works
1. The client authenticates with Google and receives a Google ID JWT.
2. Every protected API request must include this token in the header:
```
Authorization: Bearer <google-id-jwt>
```
3. The server validates the JWT signature and extracts the `sub` claim (Google User ID).
4. The `sub` value is used to look up the registered `AppUser` in the database via `AuthenticatedUserResolver`.
5. If no `AppUser` exists for that Google ID, the request is rejected with **403 Forbidden**.
### Test profile
When the application runs under the `test` Spring profile (`-Dspring.profiles.active=test`), **all security is disabled** — every endpoint is accessible without a token. This is used for automated tests only.
### User registration flow
Before a user can call any protected endpoint they must first be registered:
1. Authenticate with Google to obtain a Google ID JWT.
2. Call `POST /api/users/createUser` with the JWT's `sub` value as `googleId` and a chosen `username`.
3. All subsequent protected calls use the same JWT — the server resolves the caller automatically.
## 3. Rate Limiting
_TODO_
## 4. Endpoints
### 4.1 Home
_TODO_
### 4.2 Users
_TODO_
### 4.3 Expense Lists
_TODO_
## 5. Data Models
_TODO_
## 6. Error Handling
_TODO_
## 7. Recent Changes — `feature/security-hardening`
_TODO_