fix: accept ES256 (ECC P-256) JWT keys alongside RS256 in backend auth

Supabase JWT key was switched to ECC P-256, but the JWKS verification
only accepted RS256. Add ES256 to the accepted algorithms list.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.beans/nuzlocke-tracker-snft--support-es256-ecc-p-256-jwt-keys-in-backend-auth.md

@@ -0,0 +1,10 @@
+---
+# nuzlocke-tracker-snft
+title: Support ES256 (ECC P-256) JWT keys in backend auth
+status: in-progress
+type: bug
+created_at: 2026-03-22T10:51:30Z
+updated_at: 2026-03-22T10:51:30Z
+---
+
+Backend JWKS verification only accepts RS256 algorithm, but Supabase JWT key was switched to ECC P-256 (ES256). This causes 401 errors on all authenticated requests. Fix: accept both RS256 and ES256 in the algorithms list, and update tests accordingly.

backend/src/app/core/auth.py

@@ -60,7 +60,7 @@ def _verify_jwt_hs256(token: str) -> dict | None:
 
 
 def _verify_jwt(token: str) -> dict | None:
-    """Verify JWT using JWKS (RS256), falling back to HS256 shared secret."""
+    """Verify JWT using JWKS (RS256/ES256), falling back to HS256 shared secret."""
     client = _get_jwks_client()
     if client:
         try:
@@ -68,7 +68,7 @@ def _verify_jwt(token: str) -> dict | None:
             return jwt.decode(
                 token,
                 signing_key.key,
-                algorithms=["RS256"],
+                algorithms=["RS256", "ES256"],
                 audience="authenticated",
             )
         except jwt.InvalidTokenError:

backend/tests/test_auth.py

@@ -4,7 +4,7 @@ from uuid import UUID
 
 import jwt
 import pytest
-from cryptography.hazmat.primitives.asymmetric import rsa
+from cryptography.hazmat.primitives.asymmetric import ec, rsa
 from httpx import ASGITransport, AsyncClient
 
 from app.core.auth import AuthUser, get_current_user, require_admin, require_auth
@@ -73,6 +73,55 @@ def mock_jwks_client(rsa_key_pair):
     return mock_client
 
 
+@pytest.fixture(scope="module")
+def ec_key_pair():
+    """Generate EC P-256 key pair for testing."""
+    private_key = ec.generate_private_key(ec.SECP256R1())
+    public_key = private_key.public_key()
+    return private_key, public_key
+
+
+@pytest.fixture
+def valid_es256_token(ec_key_pair):
+    """Generate a valid ES256 JWT token."""
+    private_key, _ = ec_key_pair
+    payload = {
+        "sub": "user-456",
+        "email": "ec-user@example.com",
+        "role": "authenticated",
+        "aud": "authenticated",
+        "exp": int(time.time()) + 3600,
+    }
+    return jwt.encode(payload, private_key, algorithm="ES256")
+
+
+@pytest.fixture
+def mock_jwks_client_ec(ec_key_pair):
+    """Create a mock JWKS client that returns our test EC public key."""
+    _, public_key = ec_key_pair
+    mock_client = MagicMock()
+    mock_signing_key = MagicMock()
+    mock_signing_key.key = public_key
+    mock_client.get_signing_key_from_jwt.return_value = mock_signing_key
+    return mock_client
+
+
+async def test_get_current_user_valid_es256_token(
+    valid_es256_token, mock_jwks_client_ec
+):
+    """Test get_current_user works with ES256 (ECC P-256) tokens."""
+    with patch("app.core.auth._get_jwks_client", return_value=mock_jwks_client_ec):
+
+        class MockRequest:
+            headers = {"Authorization": f"Bearer {valid_es256_token}"}
+
+        user = get_current_user(MockRequest())
+        assert user is not None
+        assert user.id == "user-456"
+        assert user.email == "ec-user@example.com"
+        assert user.role == "authenticated"
+
+
 async def test_get_current_user_valid_token(valid_token, mock_jwks_client):
     """Test get_current_user returns user for valid token."""
     with patch("app.core.auth._get_jwks_client", return_value=mock_jwks_client):