Google App Engine Stopped Accepting Authorization Header

[Molly Dishman]

We host a node JS service on GCP (app engine). Today our normal requests to the service started to receive 400 responses saying 'Your client has issued a malformed or illegal request'. It seems that the Authorization header our client was adding may be causing the error; however, we have set that header to be allowed in our service. Is there something else we need to do for configuration in order to allow this header? It was working up until earlier today did something change in GCP? Any help would be appreciated. Thanks! 

Request example: POST to http://api/endpoint Headers (include): User-Agent, Content-Length, Content-Type, Accept, Authorization

400. That’s an error.

Your client has issued a malformed or illegal request. That’s all we know.