How I built keyless OAuth sign‑in for my AI companion

说明与用途

实现了无密钥 OAuth 登录，使用 PKCE 和单次循环回调，确保在与 Composio MCP 服务器身份验证时不在磁盘上存储任何客户端密钥或令牌。

问题

The MCP server only accepts a Bearer token from the standard OAuth flow, rejecting API keys and client secrets, so the AI companion needed a keyless sign‑in that never stores a client secret or token on disk.

结果

A fully keyless OAuth sign‑in that never writes secrets to disk, uses a single‑use loopback callback, and passes all 12 unit tests, including handling denied authorizations and missing tokens.

工作流

• Discover MCP endpoints
• Register client dynamically with token_endpoint_auth_method="none"
• Open user browser to authorize URL with PKCE and state
• Listen on 127.0.0.1:5757 for single‑use loopback callback
• Exchange code for token using PKCE verifier and resource indicator
• Store grant metadata on disk and token in OS keychain
• Close loopback listener after success or timeout

证据

The only credential it accepts is a Bearer minted by the standard MCP OAuth flow.

来源

The redirect URI is a loopback listener on 127.0.0.1 that lives only for the duration of one sign‑in (RFC 8252).

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Dynamic client registration sends token_endpoint_auth_method: "none" — no client secret is issued or stored, ever.

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The token never leaves the vault. The grant file on disk holds no secret — just grantId, the endpoint, the connected apps, and timestamps. The actual token goes to the OS keychain through the injected secret store.

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The full connect flow runs against injected fetch and URL opening in the test suite — 12 tests, all green, including "a denied authorization fails the connect instead of hanging" and "a token endpoint that returns no token is an error, not an empty grant".

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