core: Fix error when viewing used_by for built-in source

[dominic-r]

What

This PR fixes an error that occurs when trying to view the /used_by/ API endpoint for the built-in source. Previously, accessing this endpoint would raise a NotImplementedError because the built-in source doesn't properly implement the required abstract methods.

How

• Added special handling in SerializerModel.serializer to return SourceSerializer for built-in sources
• Added implementations for component, property_mapping_type, get_base_user_properties, and get_base_group_properties methods in the Source class that handle the built-in source case

Testing:

Confirmed the /api/v3/sources/all/authentik-built-in/used_by/ endpoint now returns a proper response instead of a 500 (I think) error

Closes #13587<!--
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Details

REPLACE ME

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Checklist

• Local tests pass (ak test authentik/)
• The code has been formatted (make lint-fix)

If an API change has been made

• The API schema has been updated (make gen-build)

If changes to the frontend have been made

• The code has been formatted (make web)

If applicable

• The documentation has been updated
• The documentation has been formatted (make website)

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[codecov]

Codecov Report

Attention: Patch coverage is 8.33333% with 11 lines in your changes missing coverage. Please review.

Project coverage is 92.74%. Comparing base (608f63e) to head (5a05de8).

Files with missing lines	Patch %	Lines
authentik/core/models.py	0.00%	9 Missing ⚠️
authentik/lib/models.py	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #13588      +/-   ##
==========================================
- Coverage   92.76%   92.74%   -0.03%     
==========================================
  Files         794      794              
  Lines       40577    40589      +12     
==========================================
  Hits        37643    37643              
- Misses       2934     2946      +12     

Flag	Coverage Δ
e2e	47.91% <0.00%> (-0.02%)	⬇️
integration	24.27% <0.00%> (-0.01%)	⬇️
unit	90.51% <8.33%> (-0.03%)	⬇️

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[dominic-r]

what? I didn't change docs at all. Will ignore

[rissson]

The error you're seeing is probably a symptom of a missing UsedByMixin on a serializer. Do you know which model this is failing on?

[dominic-r]

Oh my @rissson Completly forgot to answer this. I'll push a commit which should fix this issue

[dominic-r]

Verification: cURL (GET) http://localhost:9000/api/v3/sources/all/authentik-built-in/used_by/ : [] ~ In QA: Returns a server error

[rissson]

Could we add a test for this as well? I can quickly do it if you want me to

[dominic-r]

Sure, thanks