AppModule - Async HTTP Interceptors with Angular 4

app.module.ts

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { CommonModule } from '@angular/common';
import { HttpClientModule, HTTP_INTERCEPTORS } from '@angular/common/http';
import { AppComponent } from '/app.component';
import { AuthService } from './auth.service';
import { TokenInterceptor } from './token.interceptor';

@NgModule({
    declarations: [
        AppComponent
    ],
    imports: [
        BrowserModule,
        CommonModule,
        HttpClientModule
    ],
    providers: [
        AuthService,
        // register TokenInterceptor as HttpInterceptor
        {
           provide: HTTP_INTERCEPTORS,
           useClass: TokenInterceptor,
           multi: true
        }
    ]
})
export class AppModule {}