A function that returns a QR code, using the qrcode package.

qrcode.ts

/**
* ... Some lines omitted for brevity.
*/

import * as QRCode from 'qrcode';

class AuthenticationService {
    ...
    public async respondWithQRCode(data: string, response: Response) {
      QRCode.toFileStream(response, data);
    }
    ...
}