Implement SSO login

[crowesn]

Using shibboleth, implement SSO for the Treatment Database.

Example PR from ucrate: https://github.com/uclibs/ucrate/pull/1162

• Pull the tests over and get them running (failing)
• Pull over the code to turn the tests green

Need to discuss how this implementation should differ from ucrate

[Janell-Huyck]

Proposed sub-issues:

• make feature branch -Janell
• move the tests over from [the demo PR](https://ituc.service-now.com/kb? -Janell id=kb_article_view&sysparm_article=KB0011603&sys_kb_id=14fca971972bcd904f51f7afe153aff0)
• put in a ticket with IDM with a service request form to request SSO service to IDM
• check that we have endpoints and what we need for metadata and entity ID to give to IDM
• write how-to troubleshoot for Holly - how to check that the user's email matches the SSO email
• get contact information for one Public Library person to ask them to test the login with their SSO
• add gems and run bundle install
• review the demo PR and break down the code into discrete sections -Janell
• set up a development login environment vs qa vs test
• find out if we had to make server changes for scholar's SSO? We don't think there's anything on Libapps that's using SSO. - Lisa
• review using OmniAuth -Lisa
• next meeting is next Wed May 1 at 12:30 PM

[Janell-Huyck]

Pre-work PR: clean up the "registrations" controller and view. It's not being used and not planned to be used in the future. Include test clean-up. Ensure users can still edit their display names, using the User controller methods.

Note: we may be using the "registrations" controller over in Devise to register new users, with the "new" override intended just to warn people off from trying to sign up themselves.