Making sense of MCP auth

MCP authentication has evolved rapidly as the protocol expanded from trusted local servers, which generally need no authentication, to remote HTTP-based servers that require users or clients to prove their identities. The discussion distinguishes authentication, which establishes identity, from authorization, which controls permitted actions, noting that MCP focuses primarily on authentication while frameworks such as FastMCP help implement authorization policies. Early MCP guidance required server developers to operate full OAuth authorization servers, but later revisions repositioned MCP servers as protected resources that can delegate identity verification to external providers such as Okta, Google, GitHub, or self-hosted systems. Dynamic Client Registration was introduced to support agents operating from unpredictable locations but raised security and compatibility concerns, leading toward Client ID Metadata Documents, which bind client metadata to a declared URL and can restrict credential return locations. Newer work such as SEP-990 aims to support centrally managed enterprise identities and reduce repeated user sign-ins across tools. FastMCP provides OAuth proxying to connect MCP-compatible flows with conventional identity providers, issues its own tokens rather than exposing provider credentials, and can use trusted token roles and claims to hide or gate tools based on permissions. Horizon extends this model by federating identities across multiple MCP servers through a gateway, while the unresolved challenge remains defining secure identities and permissions for autonomous agents that should not necessarily inherit all of a human user’s access.

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