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());
  }
}

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?