Giving AI coding agents a public URL — the master-key delegation pattern

Your AI coding agent needs a public URL for the preview it just built. Most setup guides tell you to paste your API token into the agent's environment. That token can open unlimited tunnels, never expires, and could be exposed if the agent leaks it. There is a safer pattern that has been used across the industry for years. Full disclosure: I work with 21tunnel , one of the tunneling services that implements this pattern. While the examples use 21tunnel, the security model applies to any…