PHP判断网址是否为https函数方法，@return bool 是https返回true;否则返回false
function is_https() {
if ( !empty($_SERVER['HTTPS']) && strtolower($_SERVER['HTTPS']) !== 'off') { return true;
} elseif ( isset($_SERVER['HTTP_X_FORWARDED_PROTO']) && $_SERVER['HTTP_X_FORWARDED_PROTO'] === 'https' ) { return true;
} elseif ( !empty($_SERVER['HTTP_FRONT_END_HTTPS']) && strtolower($_SERVER['HTTP_FRONT_END_HTTPS']) !== 'off') { return true;
}else{ return false;
}
}