Allow OAuth1 callback to specify query string parameters

They are then parsed and provided to underlying HTTP package. We have to parse them so that signing of requests works properly. In addition, nonce used in the request is stored in the response so that user can verify JWT payloads returned from the server.
Can you factor this out into a helper instead of doing it twice? Maybe `splitUrl` or something that takes a url with query parameters and returns a url and a params dictionary.