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
If user unsubsrcribes from a resource that they no longer have
access to they should not be revealed the resource path, but be
redirected to app root instead.
https://gitlab.com/gitlab-org/gitlab-ce/issues/64938
