OAuth scopes don’t equal secure MCP authorization
Blog post from P0 Security
The MCP Authorization Specification leverages OAuth for broad capability scopes but faces limitations in providing the fine-grained access control necessary for secure, multi-user, role-aware systems. While OAuth scopes effectively manage high-level API privileges for delegated access, they fall short in adapting to dynamic user roles, evolving organizational policies, and context-specific permissions. OAuth tokens are static and can either become overly permissive or require issuing multiple tokens to cover policy variations. True Role-Based Access Control (RBAC) systems dynamically evaluate user roles and permissions at runtime, offering more precise and adaptable authorization. Although OAuth scopes are useful for defining coarse access boundaries, a hybrid approach that combines scopes with server-side RBAC allows for strong security, manageable tokens, and flexible policy enforcement, addressing the challenges of contextual resource access and runtime policy evaluation.