prevent duplicate user creation when characters arent entered lowercase

shared/code/tce_authorization.php

@@ -166,6 +166,10 @@ if (isset($_POST['logaction']) AND ($_POST['logaction'] == 'login') AND isset($_
 	} else {
 		// encode password
 		$xuser_password = getPasswordHash($_POST['xuser_password']);
+		//prevent users from using uppercase login names
+		if (K_AUTH_LOWERCASE_USERNAMES){
+			$_POST['xuser_name'] = strtolower($_POST['xuser_name']);
+		}
 		// check One-Time-Password if enabled
 		$otp = false;
 		if (K_OTP_LOGIN) {