feat(transport): Add server side peer cert support (#228)

* feat(transport): Add server side peer cert support

examples/src/tls_client_auth/server.rs

@@ -17,6 +17,10 @@ pub struct EchoServer;
 #[tonic::async_trait]
 impl pb::echo_server::Echo for EchoServer {
     async fn unary_echo(&self, request: Request<EchoRequest>) -> EchoResult<EchoResponse> {
+        if let Some(certs) = request.peer_certs() {
+            println!("Got {} peer certs!", certs.len());
+        }
+
         let message = request.into_inner().message;
         Ok(Response::new(EchoResponse { message }))
     }