POST /oauth/token HTTP/1.1
Host: localhost:8080
Authorization: Basic YXBwbGljYXRpb246c2VjcmV0
Content-Type: application/x-www-form-urlencoded
Cache-Control: no-cache
Postman-Token: 9f9582e9-fe73-499f-d7f7-82498a974e39

grant_type=password&username=pedroetb&password=password

let headers = new Headers();
    headers.append('Content-Type', 'application/x-www-form-urlencoded');
    headers.append("Authorization","Basic YXBwbGljYXRpb246c2VjcmV0");

    var obtainTokenUrl = 'http://localhost:8080/oauth/token';

    this._http.post(obtainTokenUrl + "?grant_type=password&username=pedroetb&password=password", null, {headers: headers}).subscribe(response => {
      console.log(response);
    });