See https://discourse.phabricator-community.org/t/fresh-install-create-admin-account-log-out-no-way-to-log-in/3090/.

It looks like a user made it to Phabricator and then logged out before addressing the "No Authentication Providers" setup issue. From here, you have to bin/auth recover your way back into your account. This is about the best we can do if they really want to log out, but we could reasonably warn users about this.