Passport Clients

You two options.

1. Allow the external system to login into your app and give them the option to create an access token for them on their account.
2. The external system can create access token using the passport endpoint like below

$http = new GuzzleHttp\Client;

$response = $http->post('http://your-app.com/oauth/token', [
    'form_params' => [
        'grant_type' => 'password',
        'client_id' => 'client-id',
        'client_secret' => 'client-secret',
        'username' => '[email protected]',
        'password' => 'my-password',
        'scope' => '',
    ],
]);

return json_decode((string) $response->getBody(), true);

Read this more info https://laravel.com/docs/5.4/passport#password-grant-tokens

just to be clear, if i choose option 2

This means i will create an API in my system lets say called (get_token), then the other system will call this API to get his Token is that what you mean ?

Route::get('get_token', function(){ $http = new GuzzleHttp\Client;

$response = $http->post('http://my-domain/oauth/token', [
    'form_params' => [
        'grant_type' => 'password',
        'client_id' => '6',
        'client_secret' => 'plNSvJpcieH8kwccJYNlTU9r4LzlliZNRk7OU5Ly',
        'username' => '[email protected]',
        'password' => 'my-password',
        'scope' => '',
    ],
]);

return json_decode((string) $response->getBody(), true);

});

If this is right then when i tried to call the API from postman i get this error

Server error: POST http://my-domain/oauth/token resulted in a 500 Internal Server Error response:\n<!--\n\n\nUnexpectedValueException: The stream or file "/var/www/html/.../storage/logs/larav (truncated...)

Your route will be

Route::post('get_token', function(Request $request){ 

$http = new GuzzleHttp\Client;

$response = $http->post('http://my-domain/oauth/token', [
    'form_params' => [
        'grant_type' => 'password',
        'client_id' => 'take_from_passport_table',
        'client_secret' => 'take_from_passport_table',
        'username' =>$request->email,
        'password' => $request->password,
        'scope' => '*',
    ],
]);

return json_decode((string) $response->getBody(), true);
});

1. Send postman POST request to http://my-domain/get_token with the parameters email & password.
2. Based on the error you posted above your storage/log/laravel.log file if not writtable so fix it as well.