Adjusting Request Headers with HttpClientModule in Angular

postServers(servers: any[]) {

  const headers = new HttpHeaders().set('Content-Type', 'application/json');

  this.http.post('https://angularsamples.firebaseio.com/data.json', servers, {
    headers: headers
  }).subscribe(value => {
    console.log(value);
  });
}

putServers(servers: any[]) {

  const headers = new HttpHeaders().set('Content-Type', 'application/json');

  this.http.put('https://angularsamples.firebaseio.com/data.json', servers, {
    headers: headers
  }).subscribe(value => {
    console.log(value);
  });
}

References
https://angular.io/guide/http#adding-headers