Open-source hallpass adds live per-user authorization checks to MCP server write operations
Adorable-Algae6903 · reddit · 2026-09-26
The author highlights a common MCP security gap: official servers like Atlassian's and GitHub's use per-user OAuth, but most self-built MCP servers — and anything touching Kubernetes, Argo CD, AWS or Vault — run on a single service account with more privileges than the person using them.
Their open-source fix, hallpass, is a small service your MCP server calls before any write: it asks the target system itself whether this user may perform this action on this resource (SubjectAccessReview for Kubernetes, IAM simulation for AWS, Argo CD RBAC, 21 systems total). Only allow proceeds; deny, unknown, or hallpass being down all mean no.
Key design points:
- One Python decorator on your tool
- User identity comes from your server's verified OAuth session, never tool arguments, so the model can't impersonate anyone
- MCP's OAuth tells you who the user is; hallpass tells you what they may do via your service token
Self-hosted, with Python and Node clients.
Related event: Open-Source hallpass Adds Real-Time Permission Checks for Agents(2 posts)→
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