Why MCP Permission Control Can't Copy API Auth
Background-Job-862 · reddit · 2026-07-13
The author reviews the pitfall of treating an MCP server like a standard internal API for permission control. Initially, they used a single shared token allowing any agent to call any tool, which led to an agent meant only to read the CRM mistakenly using a token with write access to billing tools, creating a privilege escalation risk.
They summarize the key difference between MCP permissions and standard API auth: it’s not one identity, but two—you must verify both who the agent is and which user it represents. Many permission checks must evaluate both layers simultaneously.
Their required capabilities ultimately included:
- Permission isolation at the server and tool granularity
- Separating agent identity from user identity
- Using scoped tokens that are short-lived and issued per request
The post mentions they now handle this via Truefoundry’s MCP gateway, which resolves the agent identity, checks if it can act on behalf of the user, and finally issues a token with minimum required privileges.
Related event: Pitfalls of Multi-Tenant Auth and Access Control in MCP(2 posts)→
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