fix: require password verification when user has password_hash in /auth/token

Previously the password check was gated on both user.password_hash and
request.password being truthy, so an attacker could omit the password
field (which defaults to "") and receive a valid JWT. Now any user with a
stored hash must supply a non-empty password that passes argon2 verification.

Adds six TestTokenEndpoint tests covering empty, missing, wrong, and correct
password, plus no-hash user and unknown user cases.

app/auth/router.py

@@ -44,8 +44,10 @@ async def create_token(
     if not user:
         raise HTTPException(status_code=401, detail="User not found")
 
-    # If user has password_hash, verify it
-    if user.get("password_hash") and request.password:
+    # If user has password_hash, require and verify it
+    if user.get("password_hash"):
+        if not request.password:
+            raise HTTPException(status_code=401, detail="Password required")
         try:
             from argon2 import PasswordHasher
             ph = PasswordHasher()

tests/test_auth_providers.py

@@ -37,6 +37,44 @@ def client(tmp_path):
     return TestClient(app)
 
 
+class TestTokenEndpoint:
+    """Tests for /auth/token — password bypass fix."""
+
+    def test_token_empty_password_rejected_when_user_has_hash(self, client):
+        """Empty password must be rejected when user has password_hash."""
+        resp = client.post("/auth/token", json={"email": "pw@test.com", "password": ""})
+        assert resp.status_code == 401
+
+    def test_token_missing_password_rejected_when_user_has_hash(self, client):
+        """Omitting password field (defaults to '') must be rejected when user has password_hash."""
+        resp = client.post("/auth/token", json={"email": "pw@test.com"})
+        assert resp.status_code == 401
+
+    def test_token_wrong_password_rejected(self, client):
+        """Wrong password must be rejected with 401."""
+        resp = client.post("/auth/token", json={"email": "pw@test.com", "password": "wrongpass"})
+        assert resp.status_code == 401
+
+    def test_token_correct_password_succeeds(self, client):
+        """Correct password must issue a token."""
+        resp = client.post("/auth/token", json={"email": "pw@test.com", "password": "testpass123"})
+        assert resp.status_code == 200
+        data = resp.json()
+        assert "access_token" in data
+        assert data["email"] == "pw@test.com"
+
+    def test_token_no_password_hash_user_gets_token(self, client):
+        """User without password_hash (e.g. OAuth-only user) still gets a token without a password."""
+        resp = client.post("/auth/token", json={"email": "ml@test.com"})
+        assert resp.status_code == 200
+        assert "access_token" in resp.json()
+
+    def test_token_unknown_user_rejected(self, client):
+        """Unknown email must return 401."""
+        resp = client.post("/auth/token", json={"email": "nobody@test.com", "password": "anything"})
+        assert resp.status_code == 401
+
+
 class TestPasswordAuth:
     def test_login_success(self, client):
         resp = client.post("/auth/password/login", json={