What is an MCP OAuth?

Many MCP servers act as thin wrappers around third-party APIs (a calendar, a CRM, a file store) that require the end user to authenticate and grant specific permissions. The MCP authorization spec builds this on standard OAuth 2.1 with PKCE, adding MCP-specific conventions like dynamic client registration and resource-server metadata discovery so a client can find and authenticate against a server it has never connected to before, without manual pre-configuration. The flow typically runs as: the client discovers the server requires auth, redirects the user through a browser-based consent screen, receives an authorization code, exchanges it for an access token (and refresh token), and attaches that token to subsequent MCP requests. The server never hands raw account passwords to the client, and the client never has to store anything more sensitive than a scoped, revocable token. This matters for security posture because it means access can be scoped narrowly (read-only calendar, specific workspace), audited per-token, and revoked centrally without touching the underlying account credentials at all.