Wowie, it's starting to happen! :3
When you run this in production, though, you get back the auth failure
message, and the OmniAuth logs say the server returned the following:
> invalid_client: Client authentication failed (e.g., unknown client,
> no client authentication included, or unsupported authentication
> method). The OAuth 2.0 Client supports client authentication method
> 'client_secret_post', but method 'client_secret_basic' was requested.
> You must configure the OAuth 2.0 client's
> 'token_endpoint_auth_method' value to accept 'client_secret_basic'.
I'll add a fix for this in the next commit, with some explanations as
to why!