R1:2d36afeaab7c

Manage OAuth1 request token secrets in core OAuth1 workflow

Summary:
Ref T5096. Ref T4251. See D9202 for discussion.

- Twitter seems to accept either one (?!?!?!??).
- JIRA uses RSA-SHA1, which does not depend on the token secret.
- This change makes Bitbucket work.

Test Plan:
- OAuthed with Twitter.
- OAuthed with JIRA.
- OAuthed with some Bitbucket code I had partially laying around in a partial state, which works after this change.

Reviewers: csteipp, btrahan, 20after4

Reviewed By…