/**
  * create signatures for different call types
  * @ignore
  */
 public static function init()
 {
     self::$_createCustomerSignature = array(self::$_transparentRedirectKeys, array('customer' => Braintree_Customer::createSignature()));
     self::$_updateCustomerSignature = array(self::$_transparentRedirectKeys, 'customerId', array('customer' => Braintree_Customer::updateSignature()));
     self::$_transactionSignature = array(self::$_transparentRedirectKeys, array('transaction' => Braintree_Transaction::createSignature()));
     self::$_createCreditCardSignature = array(self::$_transparentRedirectKeys, array('creditCard' => Braintree_CreditCard::createSignature()));
     self::$_updateCreditCardSignature = array(self::$_transparentRedirectKeys, 'paymentMethodToken', array('creditCard' => Braintree_CreditCard::updateSignature()));
 }