The extension service uses Envoy's ext_authz gRPC API. The backend
service for the extension must use HTTP2 or H2C as the protocol.
EXT_AUTHZ_GRPC is only supported for regional AuthzExtension resources.
ExtProcGrpc
The extension service uses ext_proc gRPC API over a gRPC stream. This is
the default value if the wire format is not specified. The backend service
for the extension must use HTTP2 or H2C as the protocol. All
supported_events for a client request are sent as part of the same
gRPC stream.