feat: support specifying a trust domain in IdentityFederation

[markgoddard]

This allows for federating with a trust domain that is not registered as
a Connect trust zone.

[github-actions]

The latest Buf updates on your PR. Results from workflow buf-ci / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	⏩ skipped	Jul 25, 2025, 2:57 PM

[gemini-code-assist]

Summary of Changes

Hello @markgoddard, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a significant enhancement to the IdentityFederation mechanism by allowing direct specification of a trust_domain for federation. This change provides greater flexibility, enabling systems to federate with external trust domains without requiring them to be pre-registered as internal Connect trust zones. The core of the change involves modifying the protobuf schema to use a oneof field, ensuring that an identity can federate via either a trust_zone_id or a trust_domain, but not both.

Highlights

• API Schema Evolution: The IdentityFederation protobuf message has been updated to use a oneof field, allowing it to specify either a trust_zone_id or a new trust_domain.
• New Federation Capability: A new trust_domain field has been introduced within the IdentityFederation message, enabling federation with trust domains that are not necessarily registered as Connect trust zones.
• Generated Code Updates: The Go (.pb.go) and TypeScript (_pb.ts) generated code for the identity.proto schema has been automatically updated to correctly reflect the new oneof structure and the trust_domain field.
• Test Data Adaptation: Existing test utility functions in pkg/connect/client/test/fakes.go were updated to correctly construct IdentityFederation objects using the new oneof pattern.

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[gemini-code-assist]

Code Review

This pull request introduces support for specifying a trust domain in IdentityFederation by changing the protobuf message to use a oneof. The changes are consistent across the protobuf definition, generated Go and TypeScript code, and test files. My main feedback is to add comments to the new protobuf fields to improve API clarity and maintainability.