[Copilot]

Add a Go token broker that uses an organization-installed GitHub App to issue Copilot inference credentials. Authorize workflows through cao.json and retrieve App private keys from Azure Key Vault; Copilot tasks remain unsupported.

• Exchange: Add /api/token-broker for gh-aw’s copilot-request protocol, using GitHub Actions OIDC authentication and least-privilege copilot_requests: read installation tokens.
• Authorization: Pin immutable owner/repository IDs and exact workflow references and revisions. Use signed check_run_id for job-scoped invalidation; deny PR, reusable-workflow and environment-based execution.
• Credentials: Read private keys through Azure managed identity. Validate installation ownership, permissions, repository scope and token expiry.
• Lifecycle: Bound request sizes, deadlines, issuance rates and encrypted credential state. Revoke tokens on job cleanup and graceful shutdown.
• Configuration: Update policy validation, TypeSpec/OpenAPI and operator documentation. Default to disabled with an empty workflow allowlist.

Initial deployment boundary: One explicitly acknowledged HTTPS process replica. Revocation state is volatile; crashes can leave issued tokens usable until expiry, capped at one hour. Live Copilot integration requires operator acceptance.