Add very basic bin/auth tool

Summary: Ref T1536. This script basically exists to restore access if/when users shoot themselves in the foot by disabling all auth providers and can no longer log in.

Test Plan: {F46411}

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1536

Differential Revision: https://secure.phabricator.com/D6205

src/applications/auth/controller/PhabricatorAuthStartController.php

@@ -47,7 +47,10 @@ final class PhabricatorAuthStartController
       return $this->renderError(
         pht(
           "This Phabricator install is not configured with any enabled ".
-          "authentication providers which can be used to log in."));
+          "authentication providers which can be used to log in. If you ".
+          "have accidentally locked yourself out by disabling all providers, ".
+          "you can use `phabricator/bin/auth recover <username>` to ".
+          "recover access to an administrative account."));
     }
 
     $next_uri = $request->getStr('next');