MCP uses OAuth 2.1 as the authorization baseline for protected remote servers. The MCP specification (revision 2026-07-28) requires authorization servers to implement OAuth 2.1, clients to implement PKCE and verify support, clients to use S256 when technically capable, and servers to implement Resource Indicators for OAuth 2.0 (RFC 8707) and validate that a token was issued specifically for them as the intended audience. Clients must apply RFC 9207 issuer validation. Client ID Metadata Documents are recommended, while Dynamic Client Registration is deprecated but retained for backward compatibility. Enterprise-Managed Authorization can centralize access provisioning through an organization’s identity provider. These controls authenticate and scope the connection; enterprises still add least-privilege business authorization, approval, and action logging above it.