example.authentication.angular.ts

//COMPONENT
this.authenticationService.login(this.f.username.value, this.f.password.value)
          .pipe(
          take(1)
          ).subscribe({

            next:() => {
              this.user.next(this.authenticationService.currentUserValue);
              this.isLoggedIn = this.authenticationService.isLoggedIn();

            },

            error:error => {
              console.error(error);
              this.errorsService.sendError(error);
              this.errorsService.registerError(error);
            }
          }
      );
//SERVICE
login(username, password) {

        let params = new HttpParams()
            .set('username', username)
            .set('password', password);

        let options = { headers: this.headers, params: params };

        // http.get() ritorna un observable quindi la funzione ritorna l'observable di http.get()
        // e nel componente mi sottoscrivo all' observable
        return this.http.get<any>(serverUrl + 'login', options)
            .pipe(
                map(data => {
                    this.setSession(data)
                    this.currentUserSubject.next(data.user)
                }),
                retry(3)
            );

    }