Simple AuthCode Generator. You can save the generated code in a database and send the code to the user. Then you can use this string to validate an email or anything you want.

AuthCode Generator

$string = "abcdefghijklmnopqrstuvwxyz0123456789"; //add as many diffrent char you need, this is the char pool.
//auth code will be 25 chars long
for($i=0;$i<25;$i++){
	$pos = rand(0,36);
	$authCode .= $string{$pos};
}
echo $authCode; //optional