# API Integration Guide

Complete guide for developers integrating applications with this OIDC Identity Provider.

---

## Table of Contents

1. [Overview](#overview)
2. [Getting Started](#getting-started)
3. [OIDC Flow](#oidc-flow)
4. [Endpoints Reference](#endpoints-reference)
5. [Client Configuration](#client-configuration)
6. [Code Examples](#code-examples)
7. [Testing](#testing)
8. [Troubleshooting](#troubleshooting)

---

## Overview

This OIDC Identity Provider implements the **Authorization Code Flow**, which is the most secure OAuth 2.0 / OpenID Connect flow suitable for server-side applications.

### What You Get

- **User Authentication**: Delegate authentication to this IdP
- **User Information**: Retrieve user profile (email, name, etc.)
- **Single Sign-On (SSO)**: Users log in once, access multiple applications
- **Secure Tokens**: RS256-signed ID tokens and access tokens

### Supported Grant Types

- ✅ Authorization Code Flow (recommended)
- ❌ Implicit Flow (not supported - insecure)
- ❌ Client Credentials (not yet implemented)
- ❌ Refresh Tokens (not yet implemented)

---

## Getting Started

### Prerequisites

1. **OIDC Provider Running**: Deploy this IdP (see [Deployment Guide](deployment.md))
2. **Admin Access**: You need admin credentials to register your application
3. **HTTPS (Production)**: Required for secure cookie handling

### Step 1: Register Your Application

1. Navigate to the admin panel: `https://your-idp.com/admin/login`
2. Log in with admin credentials
3. Go to **Clients** → **Create New Client**
4. Fill in the form:
   - **Client Name**: Your application name (e.g., "My Web App")
   - **Redirect URIs**: Where users return after login (e.g., `https://myapp.com/callback`)
   - **Allowed Scopes**: `openid profile email`

5. **Save the credentials**:
   ```
   Client ID: abc123...
   Client Secret: xyz789... (shown only once!)
   ```

### Step 2: Discover OIDC Configuration

Fetch the OIDC discovery document:

```bash
curl https://your-idp.com/.well-known/openid-configuration
```

This returns all endpoint URLs and supported features.

---

## OIDC Flow

### Authorization Code Flow (Step by Step)

```
┌─────────┐                                         ┌─────────────┐
│  User   │                                         │  Your App   │
└────┬────┘                                         └──────┬──────┘
     │                                                     │
     │  1. Click "Login"                                  │
     │───────────────────────────────────────────────────>│
     │                                                     │
     │  2. Redirect to /authorize                         │
     │<───────────────────────────────────────────────────│
     │                                                     │
┌────┴────┐                                         ┌─────┴───────┐
│  User   │                                         │  OIDC IdP   │
└────┬────┘                                         └──────┬──────┘
     │                                                     │
     │  3. Login form shown                               │
     │<───────────────────────────────────────────────────│
     │                                                     │
     │  4. Submit credentials                             │
     │───────────────────────────────────────────────────>│
     │                                                     │
     │  5. Redirect to callback with code                 │
     │<───────────────────────────────────────────────────│
     │                                                     │
┌────┴────┐                                         ┌─────┴───────┐
│  User   │                                         │  Your App   │
└────┬────┘                                         └──────┬──────┘
     │  6. Return to app                                  │
     │───────────────────────────────────────────────────>│
     │                                                     │
     │                                              ┌──────┴──────┐
     │                                              │  OIDC IdP   │
     │                                              └──────┬──────┘
     │                                                     │
     │                       7. Exchange code for tokens  │
     │                       <─────────────────────────────│
     │                                                     │
     │                       8. Return tokens             │
     │                       ─────────────────────────────>│
     │                                                     │
     │  9. Logged in!                                     │
     │<───────────────────────────────────────────────────│
     │                                                     │
```

---

## Endpoints Reference

### 1. Discovery Endpoint

**Get OIDC Configuration**

```http
GET /.well-known/openid-configuration
```

**Response:**
```json
{
  "issuer": "https://your-idp.com",
  "authorization_endpoint": "https://your-idp.com/authorize",
  "token_endpoint": "https://your-idp.com/token",
  "userinfo_endpoint": "https://your-idp.com/userinfo",
  "jwks_uri": "https://your-idp.com/jwks",
  "response_types_supported": ["code"],
  "id_token_signing_alg_values_supported": ["RS256"],
  "scopes_supported": ["openid", "profile", "email"]
}
```

---

### 2. Authorization Endpoint

**Initiate Login Flow**

```http
GET /authorize?client_id={CLIENT_ID}&redirect_uri={REDIRECT_URI}&response_type=code&scope=openid%20profile%20email&state={STATE}
```

**Parameters:**

| Parameter | Required | Description |
|-----------|----------|-------------|
| `client_id` | ✅ Yes | Your client ID |
| `redirect_uri` | ✅ Yes | Where to redirect after login (must match registered URI) |
| `response_type` | ✅ Yes | Must be `code` |
| `scope` | ✅ Yes | Space-separated scopes (must include `openid`) |
| `state` | ⚠️ Recommended | CSRF protection token (you generate this) |

**Example:**
```
https://your-idp.com/authorize?
  client_id=abc123&
  redirect_uri=https://myapp.com/callback&
  response_type=code&
  scope=openid%20profile%20email&
  state=random_csrf_token_123
```

**Response:**
User is redirected to login page. After successful login, redirected to:
```
https://myapp.com/callback?code=AUTH_CODE_HERE&state=random_csrf_token_123
```

---

### 3. Token Endpoint

**Exchange Authorization Code for Tokens**

```http
POST /token
Content-Type: application/x-www-form-urlencoded

grant_type=authorization_code&
code=AUTH_CODE&
redirect_uri=https://myapp.com/callback&
client_id=abc123&
client_secret=xyz789
```

**Parameters:**

| Parameter | Required | Description |
|-----------|----------|-------------|
| `grant_type` | ✅ Yes | Must be `authorization_code` |
| `code` | ✅ Yes | Authorization code from callback |
| `redirect_uri` | ✅ Yes | Same URI used in authorization request |
| `client_id` | ✅ Yes | Your client ID |
| `client_secret` | ✅ Yes | Your client secret |

**Response:**
```json
{
  "access_token": "eyJhbGci...",
  "token_type": "Bearer",
  "expires_in": 3600,
  "id_token": "eyJhbGci...",
  "scope": "openid profile email"
}
```

**ID Token Contents (JWT):**
```json
{
  "iss": "https://your-idp.com",
  "sub": "user-123",
  "aud": "abc123",
  "exp": 1234567890,
  "iat": 1234567890,
  "email": "user@example.com",
  "name": "John Doe",
  "preferred_username": "john"
}
```

---

### 4. UserInfo Endpoint

**Get User Information**

```http
GET /userinfo
Authorization: Bearer {ACCESS_TOKEN}
```

**Response:**
```json
{
  "sub": "user-123",
  "username": "john",
  "email": "john@example.com",
  "name": "John Doe",
  "preferred_username": "john",
  "role": "user",
  "permissions": ["read:data"]
}
```

---

### 5. JWKS Endpoint

**Get Public Keys for Token Verification**

```http
GET /jwks
```

**Response:**
```json
{
  "keys": [
    {
      "kty": "RSA",
      "use": "sig",
      "kid": "...",
      "n": "...",
      "e": "AQAB"
    }
  ]
}
```

---

## Client Configuration

### Redirect URI Rules

✅ **Allowed:**
- `https://myapp.com/callback`
- `http://localhost:8080/callback` (development only)
- `https://myapp.com/auth/oidc/callback`

❌ **Not Allowed:**
- Wildcard URIs (`https://*.myapp.com/callback`)
- Non-HTTP(S) schemes (`myapp://callback`)

### Scopes

| Scope | Description | User Info Included |
|-------|-------------|--------------------|
| `openid` | **Required** - Enables OIDC | `sub` |
| `profile` | User profile information | `name`, `preferred_username` |
| `email` | User email address | `email` |

---

## Code Examples

### Python (Flask + Authlib)

```python
from flask import Flask, redirect, url_for, session
from authlib.integrations.flask_client import OAuth

app = Flask(__name__)
app.secret_key = 'your-secret-key'

oauth = OAuth(app)
oauth.register(
    name='oidc',
    client_id='YOUR_CLIENT_ID',
    client_secret='YOUR_CLIENT_SECRET',
    server_metadata_url='https://your-idp.com/.well-known/openid-configuration',
    client_kwargs={'scope': 'openid profile email'}
)

@app.route('/login')
def login():
    redirect_uri = url_for('callback', _external=True)
    return oauth.oidc.authorize_redirect(redirect_uri)

@app.route('/callback')
def callback():
    token = oauth.oidc.authorize_access_token()
    user_info = token['userinfo']
    session['user'] = user_info
    return redirect('/')

@app.route('/')
def index():
    user = session.get('user')
    if user:
        return f"Hello, {user['name']}!"
    return '<a href="/login">Login</a>'
```

---

### Node.js (Express + Passport)

```javascript
const express = require('express');
const passport = require('passport');
const { Strategy } = require('openid-client');
const { Issuer } = require('openid-client');

const app = express();

// Discover OIDC provider
Issuer.discover('https://your-idp.com/.well-known/openid-configuration')
  .then(issuer => {
    const client = new issuer.Client({
      client_id: 'YOUR_CLIENT_ID',
      client_secret: 'YOUR_CLIENT_SECRET',
      redirect_uris: ['http://localhost:3000/callback'],
      response_types: ['code'],
    });

    passport.use('oidc', new Strategy({ client }, (tokenSet, userinfo, done) => {
      return done(null, userinfo);
    }));

    app.get('/login', passport.authenticate('oidc'));

    app.get('/callback',
      passport.authenticate('oidc', { successRedirect: '/', failureRedirect: '/login' })
    );
  });

app.listen(3000);
```

---

### PHP (Laravel Socialite)

```php
// config/services.php
'oidc' => [
    'client_id' => env('OIDC_CLIENT_ID'),
    'client_secret' => env('OIDC_CLIENT_SECRET'),
    'redirect' => env('OIDC_REDIRECT_URI'),
    'base_url' => env('OIDC_ISSUER'),
],

// routes/web.php
Route::get('/login', function () {
    return Socialite::driver('oidc')->redirect();
});

Route::get('/callback', function () {
    $user = Socialite::driver('oidc')->user();

    // $user->name
    // $user->email
    // $user->token (access token)

    Auth::login($user);
    return redirect('/dashboard');
});
```

---

### JavaScript (SPA - NOT RECOMMENDED)

⚠️ **Warning**: Authorization Code Flow requires a backend to keep the client secret secure. For SPAs, consider using **PKCE** (not yet implemented) or a backend-for-frontend (BFF) pattern.

**BFF Pattern (Recommended for SPAs):**
```
[React/Vue App] <--> [Your Node.js Backend] <--> [OIDC IdP]
                     (handles OIDC flow)
```

---

## Testing

### Manual Testing with cURL

**Step 1: Get Authorization Code**

Open in browser:
```
https://your-idp.com/authorize?client_id=test-client&redirect_uri=http://localhost:8080/callback&response_type=code&scope=openid%20profile%20email&state=test123
```

After login, you'll be redirected to:
```
http://localhost:8080/callback?code=ABC123&state=test123
```

**Step 2: Exchange Code for Token**

```bash
curl -X POST https://your-idp.com/token \
  -H "Content-Type: application/x-www-form-urlencoded" \
  -d "grant_type=authorization_code" \
  -d "code=ABC123" \
  -d "redirect_uri=http://localhost:8080/callback" \
  -d "client_id=test-client" \
  -d "client_secret=YOUR_SECRET"
```

**Step 3: Get User Info**

```bash
curl https://your-idp.com/userinfo \
  -H "Authorization: Bearer YOUR_ACCESS_TOKEN"
```

---

### Using the Test Client

This repository includes a test client:

```bash
# Start the test client
python3 test_client.py

# Open browser
open http://localhost:8080

# Click "Login with OIDC"
```

---

## Troubleshooting

### Common Errors

#### `invalid_redirect_uri`

**Problem**: The redirect URI doesn't match registered URIs.

**Solution**:
1. Check admin panel → your client → registered redirect URIs
2. Ensure exact match (including trailing slash)
3. Use URL encoding for query parameters

#### `invalid_client`

**Problem**: Client ID or secret is incorrect.

**Solution**:
1. Verify client ID and secret from admin panel
2. Check for typos or whitespace
3. Ensure client exists and is active

#### `invalid_grant`

**Problem**: Authorization code is invalid, expired, or already used.

**Solution**:
1. Authorization codes expire in 10 minutes
2. Codes can only be used once
3. Restart the flow if code expired

#### `access_denied`

**Problem**: User denied authorization or login failed.

**Solution**:
1. User may have clicked "Cancel"
2. Check credentials
3. Verify user account is active

---

### Debugging Tips

**1. Check Discovery Document**
```bash
curl https://your-idp.com/.well-known/openid-configuration | jq
```

**2. Validate ID Token**
Use [jwt.io](https://jwt.io) to decode and verify the token structure.

**3. Enable Debug Logging**
Set `LOG_LEVEL=DEBUG` in your application to see detailed OIDC flow logs.

**4. Check Server Logs**
```bash
docker-compose -f docker-compose.prod.yml logs -f oidc_server
```

---

## Security Best Practices

### ✅ Do This

- ✅ **Use HTTPS** in production (required for secure cookies)
- ✅ **Validate `state` parameter** to prevent CSRF attacks
- ✅ **Store client secret securely** (environment variables, not in code)
- ✅ **Validate ID token signature** using JWKS endpoint
- ✅ **Check token expiration** (`exp` claim)
- ✅ **Use short-lived access tokens** (default: 1 hour)
- ✅ **Implement token refresh** (when available)

### ❌ Don't Do This

- ❌ **Don't use Implicit Flow** (insecure, deprecated)
- ❌ **Don't store tokens in localStorage** (use httpOnly cookies or sessionStorage)
- ❌ **Don't expose client secret** in frontend code
- ❌ **Don't skip `state` parameter** validation
- ❌ **Don't accept tokens without verification**
- ❌ **Don't use HTTP** in production

---

## Rate Limiting

Sensitive endpoints are rate-limited:

| Endpoint | Limit |
|----------|-------|
| `/token` | 10 requests per minute |
| `/login` | 5 requests per minute |
| `/register` | 3 requests per hour |

**Response when rate-limited:**
```
HTTP 429 Too Many Requests
Retry-After: 60
```

---

## Support

- **Documentation**: [docs/](../docs/)
- **Architecture**: [ARCHITECTURE.md](ARCHITECTURE.md)
- **Deployment**: [deployment.md](deployment.md)
- **Issues**: Report bugs via GitHub issues

---

## Appendix

### Token Lifetimes

| Token Type | Default Lifetime | Configurable |
|------------|------------------|--------------|
| Authorization Code | 10 minutes | `AUTHORIZATION_CODE_LIFETIME` |
| Access Token | 1 hour | `ACCESS_TOKEN_LIFETIME` |
| ID Token | 1 hour | `ID_TOKEN_LIFETIME` |

### Supported Claims

| Claim | Description | Scope Required |
|-------|-------------|----------------|
| `sub` | User ID (unique identifier) | `openid` |
| `email` | User email address | `email` |
| `name` | User full name | `profile` |
| `preferred_username` | Display username | `profile` |
| `role` | User role | `openid` |
| `permissions` | User permissions array | `openid` |

---

**Last Updated**: 2025-11-28
**Version**: 1.0.0