App\Http\Controllers\ClientPortalController::getDocument PHP Method

    public function getDocument($invitationKey, $publicId)
    {
        if (!($invitation = $this->invoiceRepo->findInvoiceByInvitation($invitationKey))) {
            return $this->returnError();
        }
        Session::put('contact_key', $invitation->contact->contact_key);
        // track current contact
        $clientId = $invitation->invoice->client_id;
        $document = Document::scope($publicId, $invitation->account_id)->firstOrFail();
        $authorized = false;
        if ($document->expense && $document->expense->client_id == $invitation->invoice->client_id) {
            $authorized = true;
        } else {
            if ($document->invoice && $document->invoice->client_id == $invitation->invoice->client_id) {
                $authorized = true;
            }
        }
        if (!$authorized) {
            return Response::view('error', ['error' => 'Not authorized'], 403);
        }
        return DocumentController::getDownloadResponse($document);
    }