This is a follow-up question to InvalidSegmentEncoding in trying to implement “Sign in with Google” with doorkeeper-grants_assertion.

I’m trying to implement “Sign in with Google” in a Rails API application using Doorkeeper and hit a wall. I’m hoping I’m missing something obvious or there is a working example somewhere. We already have a working endpoint api/v1/users/sign_in for obtaining a token given user name and password. The controller action code for it is quite simple: