If the request wasn't initiated by gitlab we shouldn't add the new
identity to the user, and instead show that we weren't able to link
the identity to the user.
This should fix: https://gitlab.com/gitlab-org/gitlab-ce/issues/56509
As mentioned in
https://gitlab.com/gitlab-org/gitlab-ee/issues/9035#note_129093444,
Rails 5 switched ActionDispatch::Request so that it no longer inherits
Rack::Request directly. A middleware that uses Rack::Request to
read the environment may see stale request parameters if
another middleware modifies the environment via ActionDispatch::Request.
To be safe, we should be using ActionDispatch::Request everywhere.
