httpInterceptor.ts

import {Injectable} from '@angular/core';
import {HttpRequest, HttpHandler, HttpEvent, HttpInterceptor} from '@angular/common/http';
import {AuthService} from './auth/auth.service';
import {Observable} from 'rxjs/Observable';

@Injectable()
export class TokenInterceptor implements HttpInterceptor {
    constructor(public auth: AuthService) {
    }

    intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {

        request = request.clone({
            setHeaders: {
                Authorization: `Bearer ${this.auth.getToken()}`
            }
        });

        return next.handle(request);

        /* This one for manipulating Error response */

       /* return next.handle(req).do((event: HttpEvent<any>) => {
            if (event instanceof HttpResponse) {
                // do stuff with response if you want
            }
        }, (err: any) => {
            if (err instanceof HttpErrorResponse) {
                if (err.status === 401) {
                    this.auth.collectFailedRequest(request);
                }
            }
        });*/
    }
}

import { HTTP_INTERCEPTORS } from '@angular/common/http';
@NgModule({
    bootstrap: [AppComponent],
    imports: [],
    providers: [
        {
            provide: HTTP_INTERCEPTORS,
            useClass: TokenInterceptor,
            multi: true
        }
    ]
})
export class AppModule {}