is_ssl() : HTTPSプロトコルかどうかを返す

なんか大掛かりになったけど、こんなんでいいんじゃないかな…？
ツッコミほしい…。

<?php
/**
 * Determine if the protocol is HTTPS.
 * @return bool
 */
public function is_ssl()
{
    if ( isset($_SERVER['HTTPS']) === true ) // Apache
    {
        return ( $_SERVER['HTTPS'] === 'on' or $_SERVER['HTTPS'] === '1' );
    }
    elseif ( isset($_SERVER['SSL']) === true ) // IIS
    {
        return ( $_SERVER['SSL'] === 'on' );
    }
    elseif ( isset($_SERVER['HTTP_X_FORWARDED_PROTO']) === true ) // Reverse proxy
    {
        return ( strtolower($_SERVER['HTTP_X_FORWARDED_PROTO']) === 'https' );
    }
    elseif ( isset($_SERVER['HTTP_X_FORWARDED_PORT']) === true ) // Reverse proxy
    {
        return ( $_SERVER['HTTP_X_FORWARDED_PORT'] === '443' );
    }
    elseif ( isset($_SERVER['SERVER_PORT']) === true )
    {
        return ( $_SERVER['SERVER_PORT'] === '443' );
    }

    return false;
}