auth.service.ts

authenticate(username: string, password: string): Observable<any> {
  let headers = new HttpHeaders({ 'Content-Type': 'application/x-www-form-urlencoded' });
  let body = new URLSearchParams();
  body.set('username', username);
  body.set('password', password);
  body.set('grant_type', "password");
  body.set('client_id', "angular.client");
  body.set('client_secret', "secret");

  return this.http.post<any>(this.url, body.toString(), {
    headers: headers
  }).pipe(
    map(jwt => {
      if (jwt && jwt.access_token) {
        localStorage.setItem('token', JSON.stringify(jwt))
      }
    })
  );
}