Question: How to get MethodOptions from an RPC request?

[nate-meta]

I am using interceptors to perform additional validation based on the optional extensions set on an RPC on incoming and out going RPCs. Given the following gRPC schema:

extend google.protobuf.MethodOptions {
  string my_option = 50006;
}

service MyService {
  rpc Foo (FooRequest) returns (FooResponse) {
    option (my_option) = "foo"
  }
}

How do I go about getting the value of my_option? At first I had thought to get it from the request using this. However, as this is a MethodOptions it doesn't seem that its part of the descriptor. Thoughts?

[jhump]

@nate-meta: see the code example in #1526.