Authentication Flow Update

[drmmr763]

Hi @jonathanraftery

Thanks so much for this package we have been using successfully for some time.

I did just have quite a harrowing issue with Authentication. Bullhorn recently changed in June 2023 some of their authentication flows and their generic auth.bullhornstaffing urls aren't as reliable as they are. I just got off a call with one of their senior support analysts who pointed me to this documentation:

https://bullhorn.github.io/Data-Center-URLs/

I hacked the AuthClient class to change the URLs to auth-west per his recommendation. That fixed the auth issue for us. But it does mean hacking the library to resolve. Making this configurable somehow would be great.

[jonathanraftery]

It seems the ideal auth flow is to look up which auth domain should be used for the given user as shown at https://bullhorn.github.io/Getting-Started-with-REST/#determine-the-correct-data-center-for-your-user. A 307 response on sign in requests should also be handled according to that same documentation.

I'm a little surprised by this change from Bullhorn -- not sure why they couldn't update their service at the main auth domain to handle the data center lookup instead of offloading it to clients, but we'll have to handle it.

Requirements are:

1. AuthClient should be updated to look up the correct data center for the provided user and use the correct auth URLs provided from that lookup
2. 307 responses should be handled in sign in requests to redirect to the correct sign in URLs
3. (Optional) AuthClient should accept passed in domains or URLs. This would be convenient for cases where the correct data center is known beforehand, and helpful for integration tests in projects using this library as the actual library could be used (no mocking) without interacting with the 3rd-party Bullhorn service.

I can't guarantee a timeline on this update unfortunately, but will try to take care of it if I get the chance. Of course, PRs from others are always welcome as well. ;)