Google API Gateway throwing 400, Bad Request error for headers with underscore

Question

I'm using Google API Gateway (available in beta) for my service. Facing an issue with the API Requests which have API Headers with underscore (_) in it's name e.g CUSTOM_HEADER_NAME. The API Gateway throws 400, Bad Request for such requests.

The APIs work fine when the custom headers have hyphen (-) instead on underscore, e.g CUSTOM-HEADER-NAME.

It looks be to a configuration issue on the web server used by the API Gateway which is forbidding headers with underscores - Why do HTTP servers forbid underscores in HTTP header names

Since I don't have control over Google API Gateway's web server, is there a workaround to mitigate this issue and allow headers with underscores.

Note: The service is a legacy application being moved to GCP. So I don't really have the option to update the header formats as it would mean updating all the clients using this API.

Answer 1

I have reproduced the behavior you mentioned following the API Gateway quickstart and then issuing a request with underscores in headers like so curl -H "MY_HEADER: XXX" https://API-GATEWAY-URL.. I obtained the same result as yours. Therefore I have opened a feature request in the Issue Tracker so that this could be tracked.

You may be interested in examining other options such as Cloud Endpoints or Load Balancers to check if they could be an alternative in the meantime.

UPDATE: The use of underscores headers is now supported and could be achieved by adding the flag --underscore_in_headers as documented here.

Answer 2

To close the loop here, I had created a support ticket with google for supporting the headers with underscores. They obliged to the request and the changes are now available out of the box.

No changes are needed from the API Gateway users.