This commit has a fundamental flaw, in order to syncronize if external
users are still active the commit checks if the refresh token is
accepted by the OAuth provider, if that is not the case it sees that as
the user is disabled and sets the is active field to `false` to signal
that. Because it might be possible (this commit makes this a highly
likelyhood) that the OAuth provider still recognizes this user the
commit introduces code to allow users to re-active themselves via the
oauth flow if they were disabled because of this. However this code
makes no distinction in why the user was disabled and always re-actives
the user.
Thus the reactivation via the OAuth flow allows users to bypass the
manually activation setting (`[service].REGISTER_MANUAL_CONFIRM`) or if
the admin for other reasons disabled the user.
This reverts commit 21fdd28f08.
7f8f9b878f