Add debug message when denying SFTP login

sftpgo-auth.php

@@ -5,29 +5,29 @@ const DEBUG = false;
 
 require 'router.php';
 
-function deny() {
-	!DEBUG or file_put_contents(ROOT_PATH . '/db/debug.txt', ob_get_contents());
+function deny($reason) {
+	!DEBUG or file_put_contents(ROOT_PATH . '/db/debug.txt', ob_get_contents() . $reason . LF);
 	http_response_code(403);
 	exit();
 }
 
 if (CONF['common']['services']['ht'] !== 'enabled')
-	deny();
+	deny('Service not enabled.');
 
 $auth_data = json_decode(file_get_contents('php://input'), true, flags: JSON_THROW_ON_ERROR);
 
 $username = hashUsername($auth_data['username']);
 
 if (usernameExists($username) !== true)
-	deny();
+	deny('This username doesn\'t exist.');
 
 if (!in_array('ht', explode(',', query('select', 'users', ['username' => $username], 'services')[0]), true))
-	deny();
+	deny('Service not enabled for this user.');
 
 $id = query('select', 'users', ['username' => $username], 'id')[0];
 
 if (checkPassword($id, $auth_data['password']) !== true)
-	deny();
+	deny('Wrong password.');
 
 echo '
 {