authorize url controller redirects using 302 instead of 307

[mildred]

When POSTing a request to my user_*_omniauth_authorize_url, I get redirected to the OAuth endpoint using a 302 response code. This causes the request to be redirected using GET and not POST to the endpoint and makes the auth fails.

The OAuth2Strategy should redirect using the 307 response code which leaves no ambiguity that the redirect should keep the same HTTP method.