Braintree\CreditCardGateway::createSignature PHP Method

    public static function createSignature()
    {
        $options = self::baseOptions();
        $options[] = "failOnDuplicatePaymentMethod";
        $signature = self::baseSignature($options);
        $signature[] = 'customerId';
        return $signature;
    }

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