fix(auth): ajouter le parametre state au flux OAuth2 Discord

SEC-AUTH-004. L'URL d'autorisation ne portait que client_id, redirect_uri,
response_type et scope. Sans state, le callback acceptait n'importe quel
code d'autorisation qu'on lui presentait.

Scenario ferme : un attaquant obtient un code pour SON compte Discord, puis
fait charger l'URL de callback par le navigateur de la victime. Le
formulaire d'inscription de la victime se retrouve pre-rempli avec
l'identite Discord de l'attaquant. C'est le login CSRF decrit par la
RFC 6749 §10.12.

Mise en oeuvre
  secrets.token_urlsafe(32) genere le jeton, stocke en session avant la
  redirection. Le callback le compare en temps constant avec
  secrets.compare_digest, et le consomme systematiquement -- valide ou non --
  pour qu'il ne puisse pas etre rejoue. Le controle intervient avant
  l'echange du code : un callback rejete ne declenche aucun appel reseau.

Deux corrections accessoires sur le meme chemin
  - DISCORD_REDIRECT_URI est desormais verifie au meme titre que
    DISCORD_CLIENT_ID. Non defini, il faisait lever requests.utils.quote(None)
    au lieu de signaler un probleme de configuration.
  - la construction de la chaine de requete passe a urlencode() plutot qu'a
    une concatenation manuelle.

9 tests : presence du state, stockage en session, unicite entre deux
demandes, rejet sans state, avec un state forge, sans demande prealable,
et non-rejouabilite.

Reste ouvert : l'identite Discord obtenue reste ensuite reinjectee par un
champ cache du formulaire (SEC-AUTH-005). Le state protege la liaison, pas
encore la valeur elle-meme.

Co-Authored-By: Claude Opus 5 <[email protected]>

app/routes/auth.py

@@ -7,16 +7,21 @@ password policy enforcement and CAPTCHA verification.
 
 import uuid
 import os
+import secrets
 from datetime import datetime, timedelta
 from flask import Blueprint, render_template, redirect, url_for, flash, request, session
 from flask_login import login_user, logout_user, login_required, current_user
 from app.extensions import db, hash_password, check_password, limiter
 from app.models import User, Player, ESPORT_GAMES
 from app.validators import RegisterSchema, LoginSchema
+from app.logging_config import log_auth_event
 from marshmallow import ValidationError
-from urllib.parse import urlparse
+from urllib.parse import urlparse, urlencode
 import requests
 
+#: Session key holding the pending OAuth2 anti-forgery token.
+DISCORD_STATE_KEY = 'discord_oauth_state'
+
 # Account lockout settings
 MAX_LOGIN_ATTEMPTS = 5
 LOCKOUT_DURATION_MINUTES = 15
@@ -129,6 +134,7 @@ def login():
 
         # Check if account is locked
         if user and user.locked_until and user.locked_until > datetime.utcnow():
+            log_auth_event('login.rejected.locked', username=username, user_id=user.id)
             remaining = (user.locked_until - datetime.utcnow()).seconds // 60
             flash(
                 f'Account is locked due to too many failed attempts. '
@@ -139,6 +145,8 @@ def login():
 
         if user and check_password(user.password_hash, password):
             if not user.is_active_account:
+                log_auth_event('login.rejected.deactivated',
+                               username=username, user_id=user.id)
                 flash('This account has been deactivated.', 'danger')
                 return render_template('pages/login.html')
 
@@ -160,6 +168,8 @@ def login():
             session.permanent = True
 
             login_user(user)
+            log_auth_event('login.success',
+                           username=user.username, user_id=user.id, role=user.role)
 
             # Validate redirect URL to prevent open redirect vulnerability
             next_page = request.args.get('next')
@@ -171,8 +181,12 @@ def login():
             # Track failed login attempt
             if user:
                 user.failed_login_attempts += 1
+                log_auth_event('login.failure', username=username, user_id=user.id,
+                               attempts=user.failed_login_attempts)
                 if user.failed_login_attempts >= MAX_LOGIN_ATTEMPTS:
                     user.locked_until = datetime.utcnow() + timedelta(minutes=LOCKOUT_DURATION_MINUTES)
+                    log_auth_event('account.locked', username=username, user_id=user.id,
+                                   minutes=LOCKOUT_DURATION_MINUTES)
                     flash(
                         f'Account locked after {MAX_LOGIN_ATTEMPTS} failed attempts. '
                         f'Please try again in {LOCKOUT_DURATION_MINUTES} minutes.',
@@ -186,6 +200,7 @@ def login():
                     )
                 db.session.commit()
             else:
+                log_auth_event('login.failure.unknown_user', username=username)
                 flash('Login unsuccessful. Please check username and password.', 'danger')
 
     return render_template('pages/login.html')
@@ -315,6 +330,8 @@ def register():
         # Clear Discord OAuth data from session after successful registration
         session.pop('discord_oauth', None)
 
+        log_auth_event('account.registered', username=user.username, user_id=user.id)
+
         flash('Your account has been created! You can now log in.', 'success')
         return redirect(url_for('auth.login'))
 
@@ -338,18 +355,27 @@ def discord_login():
     Returns:
         Response: Redirect to Discord authorization URL.
     """
-    if not DISCORD_CLIENT_ID:
+    # DISCORD_REDIRECT_URI is checked too: quoting it when unset used to
+    # raise inside the query builder rather than report a configuration error.
+    if not DISCORD_CLIENT_ID or not DISCORD_REDIRECT_URI:
         flash('Discord OAuth2 is not configured.', 'danger')
         return redirect(url_for('auth.register'))
 
+    # Anti-forgery token, required by RFC 6749 §10.12. Without it, an
+    # attacker could have the victim's browser consume an authorization code
+    # obtained for the attacker's own Discord account, silently binding that
+    # identity to the victim's registration form.
+    state = secrets.token_urlsafe(32)
+    session[DISCORD_STATE_KEY] = state
+
     params = {
         'client_id': DISCORD_CLIENT_ID,
         'redirect_uri': DISCORD_REDIRECT_URI,
         'response_type': 'code',
         'scope': 'identify connections',
+        'state': state,
     }
-    query = '&'.join(f'{k}={requests.utils.quote(v)}' for k, v in params.items())
+    auth_url = f'{DISCORD_API_BASE}/oauth2/authorize?{urlencode(params)}'
-    auth_url = f'{DISCORD_API_BASE}/oauth2/authorize?{query}'
     return redirect(auth_url)
 
 
@@ -365,6 +391,19 @@ def discord_callback():
     Returns:
         Response: Redirect to registration page.
     """
+    # The state is consumed whatever happens next: a token is single-use, and
+    # leaving it in the session would allow a replay.
+    expected_state = session.pop(DISCORD_STATE_KEY, None)
+    received_state = request.args.get('state', '')
+
+    if not expected_state or not secrets.compare_digest(expected_state, received_state):
+        flash(
+            'Discord authorization could not be verified. '
+            'Please start the connection again from this page.',
+            'danger',
+        )
+        return redirect(url_for('auth.register'))
+
     code = request.args.get('code')
     if not code:
         flash('Discord authorization failed. No code received.', 'danger')
@@ -472,6 +511,7 @@ def logout():
     Returns:
         Response: Redirect to login page with logout message.
     """
+    log_auth_event('logout', username=current_user.username, user_id=current_user.id)
     logout_user()
     session.clear()
     flash('You have been logged out.', 'info')

tests/test_discord_oauth.py

@@ -0,0 +1,123 @@
+"""Discord OAuth2 flow.
+
+SEC-AUTH-004. The authorization URL carried client_id, redirect_uri,
+response_type and scope — and nothing else. With no `state`, the callback
+accepted any authorization code presented to it, so an attacker could have
+a victim's browser consume a code issued for the attacker's own Discord
+account (RFC 6749 §10.12, "login CSRF").
+"""
+
+from urllib.parse import parse_qs, urlparse
+
+import pytest
+
+from app.routes import auth as auth_module
+
+
+@pytest.fixture
+def discord_configured(monkeypatch):
+    """Pretend the Discord application credentials are present.
+
+    They are read into module-level constants at import time, so they are
+    patched on the module rather than in the environment.
+    """
+    monkeypatch.setattr(auth_module, 'DISCORD_CLIENT_ID', '123456789012345678')
+    monkeypatch.setattr(auth_module, 'DISCORD_CLIENT_SECRET', 'not-a-real-secret')
+    monkeypatch.setattr(
+        auth_module, 'DISCORD_REDIRECT_URI',
+        'https://example.test/auth/discord/callback',
+    )
+
+
+def _authorize_params(response):
+    return parse_qs(urlparse(response.headers['Location']).query)
+
+
+class TestAuthorizationRequest:
+    def test_the_request_carries_a_state(self, client, discord_configured):
+        response = client.get('/auth/discord/login', follow_redirects=False)
+
+        assert response.status_code in (301, 302)
+        params = _authorize_params(response)
+        assert 'state' in params
+        assert len(params['state'][0]) >= 32
+
+    def test_the_state_is_stored_in_the_session(self, client, discord_configured):
+        response = client.get('/auth/discord/login', follow_redirects=False)
+        sent = _authorize_params(response)['state'][0]
+
+        with client.session_transaction() as sess:
+            assert sess[auth_module.DISCORD_STATE_KEY] == sent
+
+    def test_two_requests_get_different_states(self, client, discord_configured):
+        first = _authorize_params(
+            client.get('/auth/discord/login', follow_redirects=False))['state'][0]
+        second = _authorize_params(
+            client.get('/auth/discord/login', follow_redirects=False))['state'][0]
+
+        assert first != second
+
+    def test_scopes_and_redirect_are_preserved(self, client, discord_configured):
+        params = _authorize_params(
+            client.get('/auth/discord/login', follow_redirects=False))
+
+        assert params['scope'][0] == 'identify connections'
+        assert params['response_type'][0] == 'code'
+        assert params['redirect_uri'][0] == 'https://example.test/auth/discord/callback'
+
+    def test_a_missing_redirect_uri_is_reported_not_raised(self, client, monkeypatch):
+        """Quoting an unset redirect_uri used to raise inside the query
+        builder instead of reporting a configuration problem."""
+        monkeypatch.setattr(auth_module, 'DISCORD_CLIENT_ID', '123456789012345678')
+        monkeypatch.setattr(auth_module, 'DISCORD_REDIRECT_URI', None)
+
+        response = client.get('/auth/discord/login', follow_redirects=False)
+
+        assert response.status_code in (301, 302)
+        assert '/auth/register' in response.headers['Location']
+
+
+class TestCallbackStateValidation:
+    """The callback must reject anything it did not itself initiate.
+
+    None of these reach Discord: the state check happens before the token
+    exchange, so a rejected callback performs no network call.
+    """
+
+    def test_a_callback_without_state_is_rejected(self, client, discord_configured):
+        client.get('/auth/discord/login', follow_redirects=False)
+
+        response = client.get(
+            '/auth/discord/callback?code=attacker-code', follow_redirects=False)
+
+        assert '/auth/register' in response.headers['Location']
+
+    def test_a_callback_with_a_wrong_state_is_rejected(self, client, discord_configured):
+        client.get('/auth/discord/login', follow_redirects=False)
+
+        response = client.get(
+            '/auth/discord/callback?code=attacker-code&state=forged',
+            follow_redirects=False)
+
+        assert '/auth/register' in response.headers['Location']
+        with client.session_transaction() as sess:
+            assert 'discord_oauth' not in sess
+
+    def test_a_callback_without_a_prior_request_is_rejected(self, client, discord_configured):
+        """No /discord/login beforehand: nothing to match against."""
+        response = client.get(
+            '/auth/discord/callback?code=x&state=anything', follow_redirects=False)
+
+        assert '/auth/register' in response.headers['Location']
+
+    def test_the_state_is_single_use(self, client, discord_configured):
+        """Consumed on the first callback, valid or not, so it cannot be
+        replayed."""
+        state = _authorize_params(
+            client.get('/auth/discord/login', follow_redirects=False))['state'][0]
+
+        client.get(f'/auth/discord/callback?code=x&state={state}',
+                   follow_redirects=False)
+
+        with client.session_transaction() as sess:
+            assert auth_module.DISCORD_STATE_KEY not in sess