The MCP call

The tool call enters through the PEP, the Policy Enforcement Point. Before it asks the PDP whether the call is allowed, the PEP checks that it is a call that can be evaluated: a well-formed MCP message, of a supported version, with a Xokepoint token, from an active agent, for an approved tool, with arguments that respect that tool's schema.

These checks are not authorization, but without them authorization would evaluate garbage. An ambiguous message could be read one way by the PEP and another way by the MCP server. A token from another issuer would bring a subject that Xokepoint does not trust. The pages of this group cover the protocol, versions and transports and token validation.