Moto (5.1.18) Server 500 Error when making a GET request to /.well-known/jwks.json for a mocked Cognito IDP user pool client app #9570
Description
When running moto server mode to test an API endpoint that does HTTPBearer validation of an access token from Cognito a 500 error is being returned by the werkzeug app.
INFO werkzeug:_internal.py:97 127.0.0.1 - - [19/Dec/2025 16:33:06] "GET /us-east-1_af38595dbbaa4e61bed9c2f41ec624f0/.well-known/jwks.json HTTP/1.1" 500 -
I'm using the fastapi-cognito library to handle the decoding and validation of access tokens. This library uses httpx to make the async request so I configure the jwks_url config setting to point to the moto server endpoint.
My implementation follows the documentation for setting up a moto server fixture:
@pytest.fixture(scope="module")
def moto_server():
"""Fixture to run a mocked AWS server for testing."""
# Note: pass `port=0` to get a random free port.
server = ThreadedMotoServer(port=0)
server.start()
host, port = server.get_host_and_port()
yield f"http://{host}:{port}"
server.stop()