gRPC prefix restricted access sounds simple. Match a method path prefix. Allow or block. Done. The problem is most implementations leave cracks. Sometimes it’s the wildcard matching rules. Sometimes the route definitions don’t align with your service names. Sometimes the check happens too late in the stack.
When your API surface grows, those cracks widen. A method like /user.Auth/Login can sneak under a looser prefix meant for /user.Public. If your gateway handles mixed HTTP and gRPC routes, you now have two worlds of rules to keep in sync. And if your service mesh does route rewrites or path normalization, what you thought you were protecting may no longer match the prefix that reaches the handler.
A good restricted access setup in gRPC must be explicit. Match full method names where possible. Prefix checks should be anchored, not partial globs. Enforce them as far upstream as possible so that no rewrites or chained interceptors can bypass the rules. Validate your service and method map against production traffic, not just local mocks. And monitor for calls hitting denied prefixes — if you see them, someone is testing your edges.