/*
 * Set user authentication for a MusicBrainz::Client object.
 *
 * This method is optional.  It only needs to be called if you want to
 * submit data to the server and give the user credit for the
 * submission.  If you want to submit data anonymously, don't call this
 * method.  Returns true if the authentication was successful.
 *
 * Aliases:
 *   MusicBrainz::Client#authenticate
 *
 * Examples:
 *   # connect as user "MrMusic", password "s3kr3tp455w0rd"
 *   mb.auth 'MrMusic', 's3kr3tp455w0rd'
 *
 *   # connect as user "MBrox", password "hithere!"
 *   mb.authenticate 'MBrox', 'hithere!'
 *
 */
static VALUE mb_client_auth(VALUE self, VALUE user, VALUE pass) {