R1:4e12a375f3f4

Add JIRA as an authentication provider

Summary:
Ref T3687. Depends on D6867. This allows login/registration through JIRA.

The notable difference between this and other providers is that we need to do configuration in two stages, since we need to generate and save a public/private keypair before we can give the user configuration instructions, which takes several seconds and can't change once we've told them to do it.

To this effect, the edit form renders two separate stages, a "setup" stage and a…