myth/auth service not working and return null

Solved.
In Linux system, paths must contain / but my local machine have Windows and in windows system paths have \ .
Just modify the psr4 paths:

In Windows server:

public $psr4 = [
APP_NAMESPACE => APPPATH, // For custom app namespace
'App'        => APPPATH, // To ensure filters, etc still found,
'Config'      => APPPATH .'Config',
'Addon'      => ROOTPATH .'addon',
'Blog'        => ROOTPATH .'addon\Blog',
'Auth'    => ROOTPATH .'addon\Auth'
];

In Linux server:

public $psr4 = [
APP_NAMESPACE => APPPATH, // For custom app namespace
'App'        => APPPATH, // To ensure filters, etc still found,
'Config'      => APPPATH .'Config',
'Addon'      => ROOTPATH .'addon',
'Blog'        => ROOTPATH .'addon/Blog',
'Auth'    => ROOTPATH .'addon/Auth'
];