MCP, AI agents, and Zero Trust: Verifying every tool call

Zero Trust for AI agents using Model Context Protocol (MCP) requires every request to be independently authenticated, validated, and authorized rather than trusted based on network location or an earlier connection. The MCP specification revision dated 2026-07-28 removes session-based trust and supports per-request, audience-bound OAuth tokens, client identity metadata, protected resource metadata, and standard 401 or 403 authorization errors, but leaves per-tool permissions, upstream delegation, auditing, and risk controls to server implementers. The guidance recommends assigning each agent a unique revocable identity, validating token issuer, signature, expiration, and intended server on every call, mapping individual tools to narrowly scoped permissions, and checking both user and agent privileges for delegated actions. It also warns against shared API keys and token passthrough to downstream APIs, recommending short-lived replacement tokens or user-specific third-party OAuth connections instead. Additional safeguards include deny-by-default behavior, private caching for caller-filtered tool lists, detailed logs of all authorization decisions, scope or authentication step-up for sensitive tasks, and human confirmation for irreversible actions. WorkOS offerings such as AuthKit, Agent Registration, FGA, Pipes, Audit Logs, and emerging enterprise controls are presented as services that can support these identity, authorization, delegation, and monitoring requirements.

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