Why does Membrane API Gateway return 500 with Error initiating OAuth2 flow?

The flowInitiator plugin could not start the OAuth2 login flow. Typical causes are a query string with a duplicate parameter, an incomplete flowInitiator configuration or an unexpected failure while creating the session or the redirect to the authorization server.

How do I fix the Error initiating OAuth2 flow error in Membrane?

Send each query parameter only once, check that oauth2, defaultFlow, triggerFlow and afterLoginUrl are set on the flowInitiator, and look at the gateway log, where Membrane logs the full exception at error level.

How do I hide the details in Membrane error responses?

Enable production mode by adding a configuration document with production: true to your apis.yaml. Membrane then leaves out detailed information from error responses.

500 Internal Server Error: Error Initiating OAuth2 Flow

Membrane API Gateway returns 500 Internal Server Error with the detail Error initiating OAuth2 flow! when the flowInitiator plugin cannot start the OAuth2 login flow for a request.

The Error Response

The response contains the status 500 Internal Server Error, the detail Error initiating OAuth2 flow!, the problem type https://membrane-api.io/problems/internal and a link to this page. The type internal means that the gateway could not complete the processing of the request. In production mode, the title is replaced by Internal Server Error and the details are left out.

What the Flow Initiator Does

The flowInitiator plugin starts an OAuth2 login on behalf of an OAuth2 client. It logs out the current session if configured, redirects the user to the authorization server and adjusts the redirect for the configured flow. It works together with the OAuth2 resource plugin it references with oauth2. For the OAuth2 flows in general, see the authorization code flow tutorial.

Common Causes

A Query Parameter Is Sent Twice

The plugin parses the query string strictly and rejects a request in which the same parameter occurs more than once, e.g. ?flow=a&flow=b.

The Configuration Is Incomplete

If the oauth2 reference to the OAuth2 resource plugin is not set, the flow cannot be started. Also check that defaultFlow, triggerFlow and afterLoginUrl are set.

The Redirect or Session Could Not Be Created

Building the redirect to the authorization server or creating the session failed. Only a few concrete causes are known for this case, so the exception in the log is the best source of information.

An Unexpected Exception in the Plugin

Any other exception that the flowInitiator plugin does not turn into an error response itself is reported under the same URL by Membrane's generic error handler. The detail then reads Aborting! Exception caused in … flow. and names the plugin, the request URI and the flow. Unless the exception points to your configuration or to the request, this usually indicates a bug in Membrane.

How to Fix It

Client side: send each query parameter only once.
Gateway operator: check the flowInitiator configuration and set oauth2, defaultFlow, triggerFlow and afterLoginUrl.
Check the gateway log. Membrane logs the full exception at error level.
If the configuration is complete, report the problem with the stack trace on GitHub Issues.

Hide Details in Production

By default, Membrane runs in development mode and adds details to error responses that help you find the problem. These details may reveal information about your setup. In production, turn them off:

configuration:
  production: true

configuration:
  production: true

Add the configuration document to your apis.yaml and separate it from the APIs with ---. The response then only contains a log key. Search the gateway log for this key to find the exception.

If the plugin is nested inside a request, response or abort element, the exception message, the stack trace and the link to this page are currently sent even in production mode. Fix the failing plugin rather than relying on production mode to hide them.