Laravel OAuth2 Server

I am new with Oauth Server.

I get this error:

ReflectionException in Container.php line 737:

Class \App\PasswordVerifier does not exist

Grant type is:

'grant_types' => [
        'password' => [
            'class' => '\League\OAuth2\Server\Grant\PasswordGrant',
            'callback' => '\App\PasswordVerifier@verify',
            'access_token_ttl' => 3600
        ]
    ],

I also create controller PasswordVerifier.

My question is where i can create PasswordVerifier class?