Summary:
Ref T13222. Ref T13231. See PHI912. I'm planning to turn MFA providers into concrete objects, so you can disable and configure them.
Currently, we only support TOTP, which doesn't require any configuration, but other provider types (like Duo or Yubikey OTP) do require some configuration (server URIs, API keys, etc). TOTP //could// also have some configuration, like "bits of entropy" or "allowed window size" or whatever, if we want.
Add concrete objects for this and standard transaction / policy / query support. These objects don't do anything interesting yet and don't actually interact with MFA, this is just skeleton code for now.
Test Plan:
{F6090444}
{F6090445}
Reviewers: amckinley
Reviewed By: amckinley
Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam
Maniphest Tasks: T13231, T13222
Differential Revision: https://secure.phabricator.com/D19935
