Summary:
Ref T1536. None of this code is reachable.
`PhabricatorAuthLoginController` provides a completely generic login/link flow, similar to how D6155 provides a generic registration flow.
`PhabricatorAuthProvider` wraps a `PhutilAuthAdapter` and glues the generic top-level flow to a concrete authentication provider.
Test Plan: Static only, code isn't meaningfully reachable.
Reviewers: btrahan
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T1536
Differential Revision: https://secure.phabricator.com/D6159
