Support for Form Post Response Mode (response_mode=form_post)

[jayrodmcneil]

Currently the service only responds with a GET response which passes the id_token as a query parameter in the URL. Software we're using only seems to support the POST response mode (reportedly for increased security), where the service winds up POSTING the id_token as a parameter back to the Service Provider.

See details here: https://openid.net/specs/oauth-v2-form-post-response-mode-1_0.html

Not a critical issue as we're only prototyping, not relying heavily on this currently, and have gotten around it by double-hopping the request through Azure AD B2C which accepts the GET method from the GCCollab IDp, and returns back to the SP with a POST response mode.

Thanks!