[X.509] Custom Header Name

[averevki]

Summary

Test X.509 authentication with a non-default XFCC header name via the new x509.source.header field.

Requires updating IdentitySection.add_mtls() in testsuite/kuadrant/policy/authorization/sections.py:111 to support the new source parameter.

Setup

• AuthPolicy with x509.source.header: "X-Custom-Client-Cert"
• Gateway configured to populate the custom header (implementation-specific)

Tests

• Verification that authentication works with a non-default XFCC header name

References

• Parent issue: E2E tests for X.509 Client Certificate Authentication in AuthPolicy (XFCC header) #885
• RFC 0015