Freelancer vs Gmail

Freelancer's API mirrors the full marketplace — projects, bids, milestones, messages, and user profiles — behind a standard OAuth 2.0 app-registration flow: a live call to `/api/users/0.1/self/` returns 401 `NOT_AUTHENTICATED` rather than any keyless access, and the OPTIONS preflight explicitly whitelists a custom `Freelancer-OAuth-V1` header, reconfirming OAuth as the real mechanism. A GET against the public `/api/projects/0.1/projects/active/` endpoint succeeds with no key at all and echoes `access-control-allow-origin: *` on both the GET and its preflight, resolving the stored 'unknown' CORS value to fully open. Freelancer's own Python SDK and developer portal document no separate paid tier or metering for the API itself — registering an app is free, with the marketplace's usual project fees applying only to actual freelance transactions, not API calls.

The Gmail API gives OAuth-scoped programmatic access to a user's mailbox: reading, searching, sending, and organizing messages, threads, labels, and drafts, with message bodies transported as base64url-encoded MIME inside JSON. It requires a Google OAuth 2.0 bearer token, confirmed live via a `WWW-Authenticate: Bearer realm="https://accounts.google.com/"` challenge on an unauthenticated request, and unlike most server-side email APIs it explicitly supports cross-origin browser calls, echoing the request Origin on both a GET and an OPTIONS preflight.