How to Debug Authentication Failures in Streamable-HTTP Mode for MCP Airflow API

When running the MCP Airflow API server with --type streamable-http, authentication failures emit specific error messages between lines 48 and 71 of src/mcp_airflow_api/mcp_main.py that indicate whether the issue stems from missing FastMCP support, absent secret keys, or token verifier construction errors.

The MCP Airflow API supports an optional Bearer token authentication layer when operating in streamable-http transport mode. Debugging authentication failures in streamable-http mode requires tracing the initialization sequence in the main entry point to identify exactly which prerequisite check is failing.

Common Causes of Authentication Failures

The source code identifies three distinct failure points during authentication initialization:

Failure Cause	Code Location	Error Message
Missing FastMCP Authentication Support	Lines 48-51 (if not HAS_AUTH_SUPPORT:)	ERROR: Bearer token authentication requested but not supported by current fastmcp version
Missing Secret Key	Lines 53-56 (if not secret_key:)	ERROR: Authentication is enabled but no secret key provided.
Token Verifier Initialization Failure	Lines 66-71 (try block with _build_static_token_auth)	ERROR: Failed to initialize StaticTokenVerifier: …

Step-by-Step Debugging Workflow

Enable Verbose Logging

Set the MCP_LOG_LEVEL environment variable to DEBUG before starting the server. The startup routine (lines 20-25) prints the chosen log level and emits detailed authentication diagnostics.

export MCP_LOG_LEVEL=DEBUG
python -m mcp_airflow_api --type streamable-http --auth-enable --secret-key my-secret

Verify Transport Type Configuration

Authentication checks only execute when transport_type == "streamable-http" (lines 46-62). If you accidentally start with stdio, authentication is bypassed entirely. Confirm the CLI flag:

python -m mcp_airflow_api --type streamable-http

Check Authentication Enablement Logic

The server resolves the final auth_enable boolean at lines 38-44. If --auth-enable is omitted, it falls back to the REMOTE_AUTH_ENABLE environment variable. Ensure this variable is set to a truthy value (true, 1, yes, or on):

export REMOTE_AUTH_ENABLE=true

If you passed --auth-enable on the CLI, the flag overrides the environment variable.

Validate Secret Key Provision

The secret key is read from --secret-key or REMOTE_SECRET_KEY (lines 44-45). A missing key triggers the error at lines 53-56. Export the variable or pass the flag:

export REMOTE_SECRET_KEY=my-super-secret

Confirm FastMCP Version Compatibility

The constant HAS_AUTH_SUPPORT indicates whether fastmcp exports StaticTokenVerifier. If False, the server aborts at lines 48-51. Upgrade the dependency:

pip install --upgrade fastmcp

Inspect Token Verifier Construction

The _build_static_token_auth(secret_key) call occurs inside a try block (lines 66-71). If this raises an exception, the error message includes the specific failure reason. Re-run with DEBUG logging to see the full traceback.

Test the Endpoint

After successful startup, verify authentication with a valid JWT:

TOKEN=$(python -c "import jwt; print(jwt.encode({'sub':'test'}, 'my-secret', algorithm='HS256'))")
curl -H "Authorization: Bearer $TOKEN" http://127.0.0.1:8000/v1/ping

A 401 response indicates the verifier rejected the token (check the JWT secret matches REMOTE_SECRET_KEY). A 200 confirms proper configuration.

Quick Diagnostic Checklist

• MCP_LOG_LEVEL set to DEBUG (lines 12-25)
• --type streamable-http explicitly passed (line 46)
• REMOTE_AUTH_ENABLE or --auth-enable is truthy (lines 38-44)
• REMOTE_SECRET_KEY or --secret-key is non-empty (lines 44-45, 53-56)
• Installed FastMCP version provides StaticTokenVerifier (HAS_AUTH_SUPPORT true, lines 48-51)
• No exception raised in _build_static_token_auth (lines 66-71)

Summary

Debugging authentication failures in streamable-http mode for the MCP Airflow API requires systematic verification of the initialization sequence in src/mcp_airflow_api/mcp_main.py. Key failure points include missing FastMCP authentication support (lines 48-51), absent secret keys (lines 53-56), and token verifier construction errors (lines 66-71). Enabling DEBUG logging and verifying environment variables REMOTE_AUTH_ENABLE and REMOTE_SECRET_KEY against the CLI flags --auth-enable and --secret-key will isolate the root cause quickly.

Frequently Asked Questions

Why does my server start without errors but still accept unauthenticated requests?

If auth_enable evaluates to False during the parsing logic at lines 38-44, the server sets mcp.auth = None (lines 72-73) and prints a warning that authentication is disabled. Verify that REMOTE_AUTH_ENABLE is set to true, 1, yes, or on, or explicitly pass --auth-enable on the command line.

What FastMCP version do I need for Bearer token authentication?

The server checks for HAS_AUTH_SUPPORT, which indicates whether fastmcp exports StaticTokenVerifier. If you encounter the error at lines 48-51, upgrade to the latest FastMCP version using pip install --upgrade fastmcp. The exact minimum version depends on when StaticTokenVerifier was introduced in the FastMCP library.

How do I generate a valid JWT token for testing the authentication?

You can generate a test token using Python's PyJWT library with the same secret key configured in REMOTE_SECRET_KEY or --secret-key. The token must use the HS256 algorithm and include standard claims like sub. Use the command: python -c "import jwt; print(jwt.encode({'sub':'test'}, 'your-secret', algorithm='HS256'))".

Why do I get a 401 error even with a valid-looking token?

A 401 response indicates that the StaticTokenVerifier successfully loaded but rejected the token signature or claims. This typically occurs when the JWT was signed with a different secret than the one provided via REMOTE_SECRET_KEY or --secret-key. Ensure the secret used to generate the token exactly matches the server's configured secret, including case sensitivity.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}