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I am trying to create a guard in order to validate if user is allowed to navigate to a route based on busines logic.

But I am getting The return type of an async function or method must be the global Promise type.ts

async canActivate(
  next: ActivatedRouteSnapshot,
  state: RouterStateSnapshot): Observable<boolean | UrlTree> | Promise<boolean | UrlTree> | boolean | UrlTree {
  const idCliente = +next.paramMap.get('id');
  const usuario = await this.authService.getUserSubject().pipe(first()).toPromise()
  const cliente = await this.clienteService.obtenerCliente(idCliente).pipe(first()).toPromise()
  return new Promise<boolean>((resolve, reject) => {
    resolve(usuario.empresaId === cliente.empresaId)
                That's correct, an async function can't return an observable, boolean or URL tree - it always returns a promise.
– jonrsharpe
                Aug 22, 2020 at 20:31
Since the return type is Promise you might want to modify the return type:
 async canActivate(next: ActivatedRouteSnapshot, state: RouterStateSnapshot): Promise<boolean> {
It would be more advisable to use Observable (rather than converting the results from both getUserSubject and obtenerCliente into Promises) as demonstrated below:
canActivate(next: ActivatedRouteSnapshot, state: RouterStateSnapshot): Observable<boolean> {
  const idCliente = +next.paramMap.get('id');
  return combineLatest(
    this.authService.getUserSubject(),
    this.clienteService.obtenerCliente(idCliente)
    .pipe(
      first(),
      map(([usuario, cliente]) => usuario.empresaId === cliente.empresaId)
        
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