NgStomp use beforeConnect in InjectableRxStompConfig

I am trying to build a angular client that uses websockets, and I am using @stomp/ng2-stompjs I am following this guide https://stomp-js.github.io/guide/ng2-stompjs/ng2-stomp-with-angular7.html

Everything works perfectly except that I need to set in the connectHeaders the token that I use to authenticate server side, to do this I read that I need to use the function beforeConnect

I tried in various way but I don't understand how to use it, it gets stuck or it sends a empty token

My rxStompConfig:

export class RxStompConfig extends InjectableRxStompConfig {

constructor(private userService: UserService) {
    super();
    this.brokerURL = env.wsServerBaseUrl;

    // Interval in milliseconds, set to 0 to disable
    this.heartbeatIncoming = 0; // Typical value 0 - disabled
    this.heartbeatOutgoing = 20000; // Typical value 20000 - every 20 seconds

    // Wait in milliseconds before attempting auto reconnect
    // Set to 0 to disable
    // Typical value 500 (500 milli seconds)
    this.reconnectDelay = 5000;
    // Will log diagnostics on console
    // It can be quite verbose, not recommended in production
    // Skip this key to stop logging to console
    this.debug = (msg: string): void => {
        console.log(new Date(), msg);
    };
    console.log('Constructor ' + this.connectHeaders);

    this.beforeConnect = (): Promise<void> => {
        return new Promise<void>((resolve, reject) => {
            this.userService.currentToken.subscribe(token => {
                console.log('Subscribed');
                if (token) {
                    console.log('Resolved ' + token);
                    this.connectHeaders = { Authorization: `Bearer ${token}`};
                    resolve();
                }
            });
        });
    };
}

I take the token from a service that does the authentication and sets the token

This is currentToken method:

get currentToken(): Observable<string> {
    return this.$token.asObservable();
}

Can someone help me on this?