message: jwt_authn: use payload struct proto directly
diff: @@ -229,14 +229,7 @@ void AuthenticatorImpl::verifyKey() {
  curr_token_->removeJwt(*headers_);
  }
  if (set_payload_cb_ && !provider.payload_in_metadata().empty()) {
  - Protobuf::util::JsonParseOptions options;
  - ProtobufWkt::Struct payload_pb;
  - const auto status =
  - Protobuf::util::JsonStringToMessage(jwt_->payload_str_, &payload_pb, options);
  - // payload_str_ have been verified as valid JSON already.
  - // All valid JSON should be able to parse into a protobuf Struct.
  - RELEASE_ASSERT(status.ok(), "Failed to parse JWT payload json into protobuf Struct");
  - set_payload_cb_(provider.payload_in_metadata(), payload_pb);
  + set_payload_cb_(provider.payload_in_metadata(), jwt_->payload_pb_);
  }
  doneWithStatus(Status::Ok);
  