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

> Debug authentication failures in streamable-http mode for MCP Airflow API. Identify missing FastMCP support, secret keys, or token issues with our guide.

- Repository: [JungJungIn/mcp-airflow-api](https://github.com/call518/mcp-airflow-api)
- Tags: how-to-guide
- Published: 2026-02-26

---

**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`](https://github.com/call518/mcp-airflow-api/blob/main/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.

```bash
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:

```bash
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`):

```bash
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:

```bash
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:

```bash
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:

```bash
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`](https://github.com/call518/mcp-airflow-api/blob/main/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.