How to encrypt the GRPC message with custom encryption before sending the data?

Question

Note : I have enough reasons to add an extra layer of security on top of TLS and using SSL certificates.

What I want to do is , before I make a grpc request , I want to encrypt the grpc request and send something like a byte array.

In google groups they gave an idea to do the following ( Link : https://groups.google.com/forum/#!msg/grpc-io/SeD6KjU5yhE/kzNd0gHgAQAJ )

message PlainChatMessage {
   string text = 1;
   int ....
}

// define your RPC request and responses using this message
message EncryptedChatMessage
{
   bytes encrypted_data = 1;
}

So , basically I need to encrypt all my PlainChatMessage request into an encrypted message. How do I implement something like this ?