Angular 5 interceptor - DI issue and solution

// DOES NOT WORK
@Injectable()
export class AuthInterceptor implements HttpInterceptor {

  constructor(
	private router: Router, private auth: Auth
  ) {}

  intercept( req: HttpRequest<any>, next: any ): Observable<HttpEvent<any>> {
    const copiedReq = req.clone({
      headers: req.headers.set(
        'authorization', 'Bearer ' + this.auth.getToken()
      )
    });
    return next.handle(copiedReq);
  }
}

// RUNTIME ERROR
compiler.js:19387 Uncaught Error: Provider parse errors:
Cannot instantiate cyclic dependency! InjectionToken_HTTP_INTERCEPTORS ("[ERROR ->]"): in NgModule AppModule in ./AppModule@-1:-1

--------
WORKING EXAMPLE

@Injectable()
export class AuthInterceptor implements HttpInterceptor {

  constructor( private injector: Injector, private router: Router) {}

  intercept( req: HttpRequest<any>, next: any ): Observable<HttpEvent<any>> {
    const auth = this.injector.get(Auth);
    const copiedReq = req.clone({
      headers: req.headers.set(
        'authorization', 'Bearer ' + auth.getToken()
      )
    });
    return next.handle(copiedReq);
  }
}