All of the GCP services implement this same API so that each service doesn't have to invent its own policy API. For example, https://github.com/googleapis/googleapis/blob/d76f26f335b2b570b7e19d938f35f9894236e565/google/genomics/v1/datasets.proto#L112 or https://github.com/googleapis/googleapis/blob/d76f26f335b2b570b7e19d938f35f9894236e565/google/spanner/admin/database/v1/spanner_database_admin.proto#L133. Anyone developing a platform with multiple gRPC services would likely need to solve this same problem.