Matillion ETL: Enhance the "Config OAuth" of type API to enable adding header parameters

Currently the Config OAuth of type “API” does not allow to add request header parameters. Some API services (like GitHub) do not return the access token response in json format, resulting in the wizard failing to successfully complete and giving the error message “OAuth token response format error”.

To resolve this, the request header parameter “Accept: Application/json” is needed.

There should be a means to present header parameters, which is what seems to be missing here.