fetch endpoint doesn't conform to the spec when an unknown sub is passed

[TakahikoKawasaki]

The current fetch endpoint implementation of spid-cie-oidc-django does not follow the OpenID Federation specification when an unknown sub is passed. In this case, the current implementation does raise Http404(), which returns a "404 Not Found" with HTML. However, to comply with the specification, the response should return JSON, not HTML, and the JSON should contain "error": "not_found".

Conceptually, a change like the one below is needed.

sed -i 's/raise Http404()/return JsonResponse({"error":"not_found","error_description":"unknown sub"},status=404)/' spid_cie_oidc/authority/views.py

[peppelinux]

Hi Sensei, thank you for this important reminder that wake me up after a long period.

In this branch I am doing all the required alignments: #324

I have decided to handle that error using invalid_subject as defined here: https://openid.net/specs/openid-federation-1_0.html#section-8.9-2.2.2.6

the branch draft-41 is a work in progress, I want to take some days to scan each section of the specification with each part of the code to complete the alignments