Make Keycloak's ID_KEY configurable

[derlin]

Proposed changes

As explained in:

• Keycloak ID_KEY should be read from settings #813

Currently, it is not possible to change the ID_KEY of the keycloak provider, even though this feature was meant to be present (according to the docstring). The ID_KEY is basically the claim used to map a user.

With this change, it is now possible to set the ID_KEY to any field present either in details or in the returned token:

SOCIAL_AUTH_KEYCLOAK_ID_KEY = "email" # use the keycloak user email (from details)
SOCIAL_AUTH_KEYCLOAK_ID_KEY = "sub" # use the keycloak user id (from token)

Types of changes

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• Release (new release request)
• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (PEP8, lint, formatting, renaming, etc)
• Refactoring (no functional changes, no api changes)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Build related changes (build process, tests runner, etc)
• Other (please describe):

Checklist

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• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works

Other information

I haven't added tests since such configurations don't seem to be tested on other backends. The default will stay exactly the same, thus not breaking the current behaviour.

Closes #813

[codecov]

Codecov Report

Merging #815 (d35b176) into master (8ac4051) will decrease coverage by 0.02%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #815      +/-   ##
==========================================
- Coverage   77.81%   77.80%   -0.02%     
==========================================
  Files         330      330              
  Lines       10093    10097       +4     
  Branches     1194     1195       +1     
==========================================
+ Hits         7854     7856       +2     
- Misses       2086     2087       +1     
- Partials      153      154       +1     

Flag	Coverage Δ
unittests	77.80% <66.66%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
social_core/backends/keycloak.py	92.59% <66.66%> (-7.41%)	⬇️

[nijel]

Merged, thanks for your contribution!