Facebook login via REST

public function facebook(Request $request)
{
    $client = new \GuzzleHttp\Client();
    $params = [
        'code'          => $request->input('code'),
        'client_id'     => $request->input('clientId'),
        'redirect_uri'  => $request->input('redirectUri'),
        'client_secret' => config('app.facebook_secret'),
    ];
    // Step 1. Exchange authorization code for access token.
    $accessTokenResponse = $client->request('GET', 'https://graph.facebook.com/v2.5/oauth/access_token', [
        'query' => $params,
    ]);
    $accessToken = json_decode($accessTokenResponse->getBody(), true);
    // Step 2. Retrieve profile information about the current user.
    $fields          = 'id,email,first_name,last_name,link,name';
    $profileResponse = $client->request('GET', 'https://graph.facebook.com/v2.5/me', [
        'query' => [
            'access_token' => $accessToken['access_token'],
            'fields'       => $fields,
        ],
    ]);
    $profile = json_decode($profileResponse->getBody(), true);

    if (empty($profile['email'])) {
        $profile['email'] = $profile['id'] . '@facebook.com';
    }
    // Step 3a. If user is already signed in then link accounts.
    if ($request->header('Authorization')) {
        $user = User::where('facebook', '=', $profile['id']);
        /*if ($user->first()) {
        return response()->json(['message' => 'There is already a Facebook account that belongs to you'], 409);
        }*/
        $token          = explode(' ', $request->header('Authorization'))[1];
        $payload        = (array) JWT::decode($token, config('app.token_secret'), array('HS256'));
        $user           = User::find($payload['sub']);
        $user->facebook = $profile['id'];
        $user->email    = $user->email ?: $profile['email'];
        $user->name     = $user->name ?: $profile['name'];
        $user->save();
        return $this->loginSuccess($user);
    }
    // Step 3b. Create a new user account or return an existing one.
    else {
        $user = User::where('facebook', '=', $profile['id']);
        if ($user->first()) {
            return $this->loginSuccess($user->first());
        }
        $user           = new User;
        $user->facebook = $profile['id'];
        $user->email    = $profile['email'];
        $user->name     = $profile['name'];
        $user->save();
        return $this->loginSuccess($user);
    }
}