FIP: Farcaster "Quick Auth" server protocol discussion #231

This FIP proposes a "Quick Auth" server that verifies Sign In with Farcaster (SIWF) credentials and issues signed JWTs, so developers avoid handling nonces, RPC state checks and session logic themselves. The article says integrating SIWF is significantly harder than integrating providers like Sign In with Google, which return a JWT that can be validated against the provider's server. The proposed open-source service would expose four endpoints: POST /nonce, POST /verify-siwf, GET /verify-jwt, and GET /.well-known/jwks.json for local verification. Tokens would carry the user's FID, the valid domain, the issuer and an expiration time, and the service could be hosted publicly at auth.farcaster.xyz or self-hosted. Its use would be optional.