[X.509] Multi-Gateway CA Isolation

[averevki]

Summary

Test isolation between gateway CA trust boundaries when multiple gateways use different CA configurations and validation tiers.

Setup

• Multiple gateways with different CA configurations and validation tiers
• Different AuthPolicies for different gateways (e.g., Tier 1 on one gateway, Tier 2 on another)

Tests

• Verify isolation between gateway CA trust boundaries

References

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