Intercepting http request/respons in Angular 2. Works from version 2.3.0.

app.module.ts

...
...
providers: [
    { provide: Http, useClass: ExtendedHttpService }
  ]
...
...

extended-http.service.ts

import { Injectable } from '@angular/core';
import { Request, XHRBackend, RequestOptions, Response, Http, RequestOptionsArgs, Headers } from '@angular/http';
import { Observable } from 'rxjs/Observable';
import { Router } from '@angular/router';
import { AuthService } from './auth/auth.service';
import 'rxjs/add/operator/catch';
import 'rxjs/add/observable/throw';

@Injectable()
export class ExtendedHttpService extends Http {

  constructor(backend: XHRBackend, defaultOptions: RequestOptions, private router: Router, private authService: AuthService) {
    super(backend, defaultOptions);
  }

  request(url: string | Request, options?: RequestOptionsArgs): Observable<Response> {
    //do whatever 
    if (typeof url === 'string') {
      if (!options) {
        options = { headers: new Headers() };
      }
      this.setHeaders(options);
    } else {
      this.setHeaders(url);
    }

    return super.request(url, options).catch(this.catchErrors());
  }

  private catchErrors() {
    return (res: Response) => {
      if (res.status === 401 || res.status === 403) {
        //handle authorization errors
        //in this example I am navigating to logout route which brings the login screen
        this.router.navigate(['logout']);
      }
      return Observable.throw(res);
    };
  }

  private setHeaders(objectToSetHeadersTo: Request | RequestOptionsArgs) {
    //add whatever header that you need to every request
    //in this example I add header token by using authService that I've created
    objectToSetHeadersTo.headers.set('Token', this.authService.getToken());
  }
}

my.service.ts

import { Injectable } from '@angular/core';
import { Http, Response } from '@angular/http';
import { Observable } from 'rxjs/Rx';

@Injectable()
export class MyService {
  constructor(private http: Http) { } // the provided ExtendedHttpService will be injected here

  getFromServer(): Observable<Whatever[]> {
    return this.http.get(WHATEVER_URL).map((res: Response) => res.json());
  }
}

I have the same as you @sirsimon.
My dependencies is ExtendedHttpService > AuthService > ExtendedHttpService. Did you find a solution?

It seems that Router cannot be injected in a service. Or at least I'm getting undefined for router when trying to navigate. Cannot find name 'Router'. Going back to window.location.href :(

I ran into the same issue today. As soon as anything inside authService has Http as a dependency you get a cyclic dependency error. Did anybody come up with a solution to this?

@miczed It's because in your @NgModule you import HttpModule which already incluse Http.
So in the provider, you must use a factory :

providers: [
...
{
      provide: Http,
      useFactory: (backend: XHRBackend, options: RequestOptions, tokenService: TokenService, router: Router) => {
        return new ExtendedHttpService(backend, options, authService, router);
      },
      deps: [XHRBackend, RequestOptions, AuthService, Router]
   }
]
...

Just adding to the answer by @mvkirk :

Using @angular/core 2.4.8, this returns the following error:

ERROR in Error encountered resolving symbol values statically. Function calls are not supported. Consider replacing the function or lambda with a reference to an exported function (position XX:XX in the original .ts file), resolving symbol AppModule in ...XX/app.module.ts

To curb this, create a seperate file for the factory, as described here:
https://pub.scotch.io/@kashyapmukkamala/using-http-interceptor-with-angular2

Has this been tested with the latest version of Angular? (4.0.3)
I cannot seem to navigate anywhere once inside the if block (L35).

nm...The issue seems to be L37. I'm using Angular 4.0.3 and if you return Observable.throw, navigation will not work, but using .of instead allows the navigation to continue. See my gist

I can't get 401 error from one of my cakephp server, just from a node server, why? on the browser have 401 error, but headers,response from angular give me status =0, i'm using jwt and angular 4.1

This problem is very well explained on StackOverflow's question page. Personally, I'm do not like approach which is listed there as an accepted answer, but it's completely obvious that injector must be used on one way or another.

Just implemented this, works great nice and simple. Great platform to build your own logic off.

Good job man. You saved my lot of time.

How we can use same into angular 6?