public static void Reset(string appKey, string appSecret, string authToken)
 {
     _authToken = authToken;
     _appKey    = appKey;
     _appSecret = appSecret;
     instance   = null;
 }
 public static void Reset(string appKey, string appSecret)
 {
     _appKey    = appKey;
     _appSecret = appSecret;
     instance   = null;
 }
 public static void Reset(string authToken)
 {
     _authToken = authToken;
     instance   = null;
 }