Understanding OAuth 2.1 for MCP (Model Context Protocol) Servers: Discovery, Authorization, and Access Phases

OAuth 2.1 has been officially adopted as the mandated authorization standard within the Model Context Protocol (MCP) specifications, emphasizing enhanced security measures for both confidential and public clients. This integration enables MCP to facilitate transport-level authorization, allowing clients to securely access restricted servers on behalf of resource owners through a modern, standardized framework that prioritizes security and interoperability. The MCP authorization flow leverages OAuth 2.1's capabilities across three key phases: discovery, registration, and authorization. During discovery, clients obtain server metadata via a 401 Unauthorized response with a WWW-Authenticate header, enabling them to understand