Laravel unit tests - passing in authorization token as header

I'm trying to pass an auth token as a header but the token is not being registered, therefore I am being blocked from my request.

1) Make initial request for auth token:

    $response = $this->call('POST', 'oauth/access_token', [
        //data to get auth token
    ]);

    //valid token       
    $access_token = json_decode($response->content())->access_token; 

2) Make request for data, using the auth token as a header. Reading this message chain on this topic, I thought that this was the way to do it:

    $activities = $this->call('GET', '1.0/stuff', [],
        [
            Request::header('Authorization') => $access_token
        ]
    );

3) Print out the result:

    die($activities); 

Command line response: {"error":"forbidden","error_description":"Access denied.","error_data":null}

What is the correct way to pass headers in Laravel-5 phpunit testing?

via Chebli Mohamed