This function extracts the oauth parameters from a req, and returns them as a List[Tuple2[String,String]]. This function is useful for extracting the nonce, timestamp, signature etc from a signed request, but will also return all the other parameters used in the signature generation. req should be either a code_data_generic_ApiRequest or a code_model_flows_processors_http_HttpRequest. headerName is not mandatory and defaults to "Authorization". oauthHeaderPrefix is not mandatory and defaults to "Oauth".