protected static function _signature($data, $secret = null) {
		unset($data['__signature']);
		$secret = ($secret) ?: static::$_secret;
		return hash_hmac('sha1', serialize($data), $secret);
	}
protected static function _signature($data, $secret = null) {
		unset($data['__signature']);
		$secret = ($secret) ?: static::$_secret;
		return hash_hmac('sha1', serialize($data), $secret);
	}
protected static function _signature ( $ data , $ secret = null ) { unset ( $ data [ '__signature' ] ) ; $ secret = ( $ secret ) ? : static :: $ _secret ; return hash_hmac ( 'sha1' , serialize ( $ data ) , $ secret ) ; }
Calculate the HMAC signature based on the data and a secret key.

@param mixed $data
@param null|string $secret Secret key for HMAC signature creation.
@return string HMAC signature.
Calculate the HMAC signature based on the data and a secret key .