getIpAddress() {
  return this.http.get<{ ip: string }>('https://jsonip.com/');
}

ipAddress: any;

...

getIp() {
  this.ipService.getIpAddress()
  .subscribe(data => {
    return this.ipAddress = data['ip'];
  });
}

<input
    matInput
    placeholder="Indirizzo IP"
    formControlName="lastIp"
    [errorStateMatcher]="matcher"
    [(ngModel)]="ipAddress"
    [readonly]="true">

app.use((req, res, next) => {
  res.setHeader('Access-Control-Allow-Origin', '*');
  res.setHeader('Access-Control-Allow-Methods', 'GET, POST, OPTIONS, PUT, PATCH, DELETE');
  res.setHeader('Access-Control-Allow-Headers', 'Origin, X-Requested-With, Accept, Authorization, Content-Type');
  res.setHeader('Access-Control-Allow-Credentials', true);
  next();
});