R1:25e43e872bb6

Add Twitter as an authentication provider

Summary: Ref T3687. Depends on D6864. Implements the `OAuth1` provider in Phabricator (which is mostly similar to the OAuth2 provider, but doesn't share quite enough code to actually extend a common base class, I think) and Twitter as a concrete subclass.

Test Plan:
Created a Twitter provider. Registered, logged in, linked, refreshed account link.

{F57054}

{F57056}

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3687

Differential…