add middleware to rewrite the /.well-known/openid-configuration endpoint for external idps

[wkloucek]

Description

We've added the configuration option PROXY_OIDC_REWRITE_WELLKNOWN to rewrite the /.well-known/openid-configuration endpoint.
If active, it serves the /.well-known/openid-configuration response of the original IDP configured in OCIS_OIDC_ISSUER / PROXY_OIDC_ISSUER. This is needed so that the Desktop Client, Android Client and iOS Client can discover the OIDC identity provider.

Previously this rewrite needed to be performed with an external proxy as NGINX or Traefik if an external IDP was used.

Related Issue

• Fixes simplify oCIS deployment with external IDP #2819
• Fixes Unable to sign-in with native apps with OIDC #3280
• Unblocks add feature flag for external user management ocis-charts#58

Motivation and Context

How Has This Been Tested?

• locally
• deployment examples (see changes)

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Technical debt
• Tests only (no source changes)

Checklist:

• Code changes
• Unit tests added
• Acceptance tests added
• Documentation ticket raised:

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would create a changelog item based on your changes.

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

0.0% Coverage
0.0% Duplication