How can I add tags per request?

I have this working, but i need to pass in a couple specific tags like username etc so i know who the trace is for. I don't see a way to do that. I am referring to the express implementation. i will have custom fields added to the request object...

was thinking maybe I could do a pull request that looks for a 'tags' object on the request object, and if that's there it adds to the span? if not then nobody breaks and it's backwards compatible?