Add docs for how to set up federated logins

[hmpf]

This is quite rough and ready. Each provider will have very different steps so we cannot go into high detail on any of them.

[github-actions[bot]]

Test results

       7 files     588 suites   22m 29s :stopwatch:    469 tests    468 :heavy_check_mark: 1 :zzz: 0 :x: 3 283 runs  3 276 :heavy_check_mark: 7 :zzz: 0 :x:

Results for commit 463f395b.

:recycle: This comment has been updated with latest results.

[sonarqubecloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 84.50%. Comparing base (5025523) to head (463f395). Report is 12 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #803      +/-   ##
==========================================
- Coverage   84.58%   84.50%   -0.08%     
==========================================
  Files          75       76       +1     
  Lines        3762     3808      +46     
==========================================
+ Hits         3182     3218      +36     
- Misses        580      590      +10     

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