code: public String getHttpHeaderBasicKey() throws Exception {
          if (root.getConfig().getClientId() == null || root.getConfig().getClientId().length() == 0)
              throw new Exception ("MangoPay.config.ClientId is not set.");
          
          if (root.getConfig().getClientPassword() == null || root.getConfig().getClientPassword().length() == 0)
              throw new Exception ("MangoPay.config.ClientPassword is not set.");
          
          String signature = root.getConfig().getClientId() + ':' + root.getConfig().getClientPassword();
          
          return Base64Encoder.encode(signature);
      }
docs: Gets basic key for HTTP header.
  @return  Authorization string.
  @throws Exception