app-initializer.ts

export function appInitializer(authService: AuthService) {
  return () =>
    new Promise((resolve) => {
      console.log('refresh token on app start up')
      authService.refreshToken().subscribe().add(resolve);
    });
}

This method won't work in Rxjs included in Angular 13. We can refactor the interceptor like this:

export function appInitializer(authService: AuthService) {
  return () =>
    new Promise((resolve) => {
      console.log('refresh token on app start up')
      return () => firstValueFrom(authService.refreshToken());
    });
}

Also don't use:

return authService.refreshToken().toPromise()

This method is depracated and will be removed soon.

Hi @Krzysztofz01 , thank you for pointing it out.
I have updated the solution to Angular v13.
Please check my Git repo for details.

https://github.com/dotnet-labs/JwtAuthDemo/blob/51ef91c75bed8538c62700014c0ad828f63d486a/angular/src/app/core/services/app-initializer.ts#L4-L8