A basic UDP proxy used to bypass client-side Xbox Live authentication in MCPE 1.2.

run.php

<?php

/*
 *
 *  ____            _        _   __  __ _                  __  __ ____
 * |  _ \ ___   ___| | _____| |_|  \/  (_)_ __   ___      |  \/  |  _ \
 * | |_) / _ \ / __| |/ / _ \ __| |\/| | | '_ \ / _ \_____| |\/| | |_) |
 * |  __/ (_) | (__|   <  __/ |_| |  | | | | | |  __/_____| |  | |  __/
 * |_|   \___/ \___|_|\_\___|\__|_|  |_|_|_| |_|\___|     |_|  |_|_|
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * @author PocketMine Team
 * @link http://www.pocketmine.net/
 *
 *
*/

declare(strict_types=1);

$bindAddr = "0.0.0.0";
$bindPort = 19132;


echo "Enter server address: ";
$serverAddress = gethostbyname(trim(fgets(STDIN)));
echo "Enter server port: ";
$serverPort = (int) trim(fgets(STDIN));
if($serverPort !== 19132){
	echo "Warning: You may experience problems connecting to PocketMine-MP servers on ports other than 19132 if the server has port checking enabled." . PHP_EOL;
}

echo "Opening socket... ";
$sock = socket_create(AF_INET, SOCK_DGRAM, SOL_UDP);
if(!socket_bind($sock, $bindAddr, $bindPort)){
	echo "[!] Can't bind to $bindAddr on port $bindPort, is something already using that port?" . PHP_EOL;
	exit(1);
}
socket_set_option($sock, SOL_SOCKET, SO_SNDBUF, 1024 * 1024 * 8);
socket_set_option($sock, SOL_SOCKET, SO_RCVBUF, 1024 * 1024 * 8);

echo "Sending ping to server on $serverAddress $serverPort... ";
$ping = "\x01" . pack("NN", mt_rand(0, 0x7fffffff), mt_rand(0, 0x7fffffff)) . "\x00\xff\xff\x00\xfe\xfe\xfe\xfe\xfd\xfd\xfd\xfd\x12\x34\x56\x78";
socket_sendto($sock, $ping, strlen($ping), 0, $serverAddress, $serverPort);

$pong = "";
echo "Waiting for communication... ";
while(true){
	$len = socket_recvfrom($sock, $pong, 65535, 0, $addr, $port);
	if($addr === $serverAddress and $port === $serverPort and $pong{0} === "\x1c"){
		echo "Got ping response from server!" . PHP_EOL;
		break;
	}
}

echo "Waiting for client ping..." . PHP_EOL;
$len = socket_recvfrom($sock, $buffer, 65535, 0, $clientAddr, $clientPort);
echo "Got ping from $clientAddr on port $clientPort!" . PHP_EOL;
socket_sendto($sock, $pong, strlen($pong), 0, $clientAddr, $clientPort);

echo "Waiting for client connection..." . PHP_EOL;
while(true){
	$len = socket_recvfrom($sock, $buffer, 65535, 0, $clientAddr, $clientPort);
	if($buffer{0} === "\x05"){ //OpenConnectionRequest1
		echo "Got connection from $clientAddr on port $clientPort!" . PHP_EOL;
		break;
	}
	// FIXME: We aren't relaying this connection request. Not really a problem since RakNet will resend it with the same MTU a few times, but shouldn't we relay this anyway?
}

echo "Packets from this address are now being relayed to $serverAddress on port $serverPort" . PHP_EOL;
echo "Press CTRL+C to stop the proxy." . PHP_EOL;

socket_set_option($sock, SOL_SOCKET, SO_RCVTIMEO, ["sec" => 10, "usec" => 0]);

while(true){
	$status = @socket_recvfrom($sock, $buffer, 65535, 0, $source, $port);
	if($status !== false){
		//echo "Got packet from $source $port: " . bin2hex($buffer) . PHP_EOL;
		if($source === $serverAddress and $port === $serverPort){
			//echo "Got packet from server: " . bin2hex($buffer) . PHP_EOL;
			socket_sendto($sock, $buffer, strlen($buffer), 0, $clientAddr, $clientPort);
		}elseif($source === $clientAddr and $port === $clientPort){
			//echo "Got packet from client: " . bin2hex($buffer) . PHP_EOL;
			socket_sendto($sock, $buffer, strlen($buffer), 0, $serverAddress, $serverPort);
		}else{
			//echo "Ignored packet from $source $port" . PHP_EOL;
			continue;
		}
	}elseif(socket_last_error($sock) === SOCKET_ETIMEDOUT){
		echo "No communications received from server or client within 10 seconds. Exiting." . PHP_EOL;
		break;
	}
}