negotiateendpoint along with generated UUID in
x-tezos-live-useridHTTP header will return
accessTokenin the response, which you will use for SignalR hub connection.
For generating UUIDs you can use any library, that complies with RFC4122. For example https://www.npmjs.com/package/uuid. You can also use different method for generating userIds, as long as you can ensure, that each client will have unique id.