POST form Angular2

I'm trying to execute a login form with Angular2 with NodeJS API as a backend server.

I cant't post any request to the API. Here it's my front code example:

private authenticate_url = "Server_URL:PORT/authenticate";
login(username: string, password: string): Observable<User> {
    let headers = new Headers({ 'Content-Type': 'application/json' });
    let options = new RequestOptions({ headers: headers });
    console.log("Username : "+username+" Password : "+password);
    return this.http.post(this.authenticate_url, { username, password }, options)
                .map(this.extractData)
                .catch(this.handleError)
}

Either when I'm checking network activity, no POST request was executed.

via BenChaaben Tarek