Master-Key Delegation Pattern Offers Safer Way to Grant AI Agents Tunnel Access

AI coding agents like Claude Code, Cursor, and Devin often need a public URL to expose localhost for testing webhooks or previewing apps, but sharing a permanent API token with these agents poses serious security risks. A safer approach called the master-key delegation pattern allows a long-lived master key to mint short-lived, scoped child keys that are handed to the agent instead. Child keys expire automatically, are limited to a single project, and cannot generate further credentials, minimising potential damage if exposed. Revoking the master key instantly invalidates all child keys it created, enabling quick recovery from a compromise. The model mirrors established industry practices used by Stripe Restricted Keys, AWS STS, GitHub Fine-Grained Tokens, and HashiCorp Vault, applying the principle that long-lived credentials should only ever create short-lived ones.