Laravel/Passport doesn't redirect back to authorization form after login

Here is how I handle the login in my Laravel app:

public function authenticate(Request $request)
{
    $validator = Validator::make($request->all(), [
        'email' => 'required|email',
        'password' => 'required',
    ]);

    if ($validator->passes()) {
        $credentials = array(
            'email' => $request->email,
            'password' => hash('sha512', $request->password)
        );

        if (User::where($credentials)->exists()) {
            $user = User::where($credentials)->first();
            Auth::login($user, isset($request->remember));
            return redirect()->back()->withInput($request);
        } else {
            return redirect()->route('login');
        }
    } else {
        return redirect()->route('login', ['error' => $validator->errors()->first()]);
    }
}

And here is how I initiate the Authorize method of Laravel Passport:

public function auth(Request $request)
{
    $request->session()->put('state', $state = Str::random(40));

    $query = http_build_query([
        'client_id' => '3',
        'redirect_uri' => 'http://127.0.0.1:8000/authorize/response',
        'response_type' => 'code',
        'scope' => '',
        'state' => $state
    ]);

    return redirect('http://127.0.0.1:9000/oauth/authorize?'.$query);
}

So basically when I run auth function and I am not logged in when I nabvigate to http://127.0.0.1:9000/oauth/authorize.... url I get redirected to the Login route of my app. That's fine I need to login to authorize the permission. So far so good.

The problem is that after I login successfully I don't get redirected back to http://127.0.0.1:9000/oauth/authorize... URL. Why?

How can I fix that so that after I login I get directly redirected back to the Authorization prompt?