一些常用函数

1，随机生成auth_key

function build_auth_key()
{
    $chars = 'abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ';
    // $chars .= '`~!@#$%^&*()_+-=[]{};:"|,.<>/?';
    $chars = str_shuffle($chars);
    return substr($chars, 0, 40);
}