Handling 401s globally with Angular

Question

In my Angular 2 project I make API calls from services that return an Observable. The calling code then subscribes to this observable. For example:

getCampaigns(): Observable<Campaign[]> {
    return this.http.get('/campaigns').map(res => res.json());
}

Let's say the server returns a 401. How can I catch this error globally and redirect to a login page/component?

Thanks.

---

Here's what I have so far:

// boot.ts

import {Http, XHRBackend, RequestOptions} from 'angular2/http';
import {CustomHttp} from './customhttp';

bootstrap(AppComponent, [HTTP_PROVIDERS, ROUTER_PROVIDERS,
    new Provider(Http, {
        useFactory: (backend: XHRBackend, defaultOptions: RequestOptions) => new CustomHttp(backend, defaultOptions),
        deps: [XHRBackend, RequestOptions]
    })
]);

// customhttp.ts

import {Http, ConnectionBackend, Request, RequestOptions, RequestOptionsArgs, Response} from 'angular2/http';
import {Observable} from 'rxjs/Observable';

@Injectable()
export class CustomHttp extends Http {
    constructor(backend: ConnectionBackend, defaultOptions: RequestOptions) {
        super(backend, defaultOptions);
    }

    request(url: string | Request, options?: RequestOptionsArgs): Observable<Response> {

        console.log('request...');

        return super.request(url, options);        
    }

    get(url: string, options?: RequestOptionsArgs): Observable<Response> {

        console.log('get...');

        return super.get(url, options);
    }
}

The error message I'm getting is "backend.createConnection is not a function"

Answer 1

Angular 4.3+

With the introduction of HttpClient came the ability to easily intercept all requests / responses. The general usage of HttpInterceptors is well documented, see the basic usage and how to provide the interceptor. Below is an example of an HttpInterceptor that can handle 401 errors.

Updated for RxJS 6+

import { Observable, throwError } from 'rxjs';
import { HttpErrorResponse, HttpEvent, HttpHandler,HttpInterceptor, HttpRequest } from '@angular/common/http';

import { Injectable } from '@angular/core';
import { catchError } from 'rxjs/operators';

@Injectable()
export class ErrorInterceptor implements HttpInterceptor {

  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    return next.handle(req).pipe(
      catchError((err: HttpErrorResponse) => {
        if (err.status == 401) {
          // Handle 401 error
        } else {
          return throwError(err);
        }
      })
    );
  }

}

RxJS <6

import { Injectable } from '@angular/core';
import { HttpInterceptor, HttpRequest, HttpHandler, HttpEvent, HttpErrorResponse } from '@angular/common/http'
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/do';

@Injectable()
export class ErrorInterceptor implements HttpInterceptor {

    intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
        return next.handle(req).do(event => {}, err => {
            if (err instanceof HttpErrorResponse && err.status == 401) {
                // handle 401 errors
            }
        });
    }
}

Answer 2

Description

The best solution I have found is to override the XHRBackend such that the HTTP response status 401 and 403 leads to a particular action.

If you handle your authentication outside your Angular application you could force a refresh of the current page such that your external mechanism is triggered. I detail this solution in the implementation below.

You could also forward to a component inside your application such that your Angular application is not reloaded.

Implementation

Angular > 2.3.0

Thanks to @mrgoos, here is a simplified solution for angular 2.3.0+ due to a bug fix in angular 2.3.0 (see issue https://github.com/angular/angular/issues/11606) extending directly the Http module.

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


@Injectable()
export class AuthenticatedHttpService extends Http {

  constructor(backend: XHRBackend, defaultOptions: RequestOptions) {
    super(backend, defaultOptions);
  }

  request(url: string | Request, options?: RequestOptionsArgs): Observable<Response> {
    return super.request(url, options).catch((error: Response) => {
            if ((error.status === 401 || error.status === 403) && (window.location.href.match(/\?/g) || []).length < 2) {
                console.log('The authentication session expires or the user is not authorised. Force refresh of the current page.');
                window.location.href = window.location.href + '?' + new Date().getMilliseconds();
            }
            return Observable.throw(error);
        });
  }
}

The module file now only contains the following provider.

providers: [
    { provide: Http, useClass: AuthenticatedHttpService }
]

Another solution using Router and an external authentication service is detailed in the following gist by @mrgoos.

Angular pre-2.3.0

The following implementation works for Angular 2.2.x FINAL and RxJS 5.0.0-beta.12.

It redirects to the current page (plus a parameter to get a unique URL and avoid caching) if an HTTP code 401 or 403 is returned.

import { Request, XHRBackend, BrowserXhr, ResponseOptions, XSRFStrategy, Response } from '@angular/http';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/catch';
import 'rxjs/add/observable/throw';

export class AuthenticationConnectionBackend extends XHRBackend {

    constructor(_browserXhr: BrowserXhr, _baseResponseOptions: ResponseOptions, _xsrfStrategy: XSRFStrategy) {
        super(_browserXhr, _baseResponseOptions, _xsrfStrategy);
    }

    createConnection(request: Request) {
        let xhrConnection = super.createConnection(request);
        xhrConnection.response = xhrConnection.response.catch((error: Response) => {
            if ((error.status === 401 || error.status === 403) && (window.location.href.match(/\?/g) || []).length < 2) {
                console.log('The authentication session expires or the user is not authorised. Force refresh of the current page.');
                window.location.href = window.location.href + '?' + new Date().getMilliseconds();
            }
            return Observable.throw(error);
        });
        return xhrConnection;
    }

}

with the following module file.

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { HttpModule, XHRBackend } from '@angular/http';
import { AppComponent } from './app.component';
import { AuthenticationConnectionBackend } from './authenticated-connection.backend';

@NgModule({
    bootstrap: [AppComponent],
    declarations: [
        AppComponent,
    ],
    entryComponents: [AppComponent],
    imports: [
        BrowserModule,
        CommonModule,
        HttpModule,
    ],
    providers: [
        { provide: XHRBackend, useClass: AuthenticationConnectionBackend },
    ],
})
export class AppModule {
}

Answer 3

As frontend APIs expire faster than milk, with Angular 6+ and RxJS 5.5+, you need to use pipe:

import { HttpInterceptor, HttpEvent, HttpRequest, HttpHandler, HttpErrorResponse } from '@angular/common/http';
import { Observable, throwError } from 'rxjs';
import { Injectable } from '@angular/core';
import { catchError } from 'rxjs/operators';
import { Router } from '@angular/router';

@Injectable()
export class AuthInterceptor implements HttpInterceptor {

  constructor(private router: Router) { }

  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    return next.handle(req).pipe(
      catchError((err: HttpErrorResponse) => {
        if (err.status === 401) {
          this.router.navigate(['login'], { queryParams: { returnUrl: req.url } });
        }
        return throwError(err);
      })
    );
  }
}

Update for Angular 7+ and rxjs 6+

import { HttpRequest, HttpHandler, HttpEvent, HttpInterceptor, HttpErrorResponse } from '@angular/common/http';
import { Observable, of } from 'rxjs';
import { Injectable } from '@angular/core';
import { catchError } from 'rxjs/internal/operators';
import { Router } from '@angular/router';

@Injectable()
export class AuthInterceptor implements HttpInterceptor {

  constructor(private router: Router) { }

  intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    return next.handle(request)
      .pipe(
        catchError((err, caught: Observable<HttpEvent<any>>) => {
          if (err instanceof HttpErrorResponse && err.status == 401) {
            this.router.navigate(['login'], { queryParams: { returnUrl: request.url } });
            return of(err as any);
          }
          throw err;
        })
      );
  }
}

Answer 4

The Observable you get from each request method is of type Observable<Response>. The Response object, has an status property which will hold the 401 IF the server returned that code. So you might want to retrieve that before mapping it or converting it.

If you want to avoid doing this functionality on each call you might have to extend Angular 2's Http class and inject your own implementation of it that calls the parent (super) for the regular Http functionality and then handle the 401 error before returning the object.

See:

https://angular.io/docs/ts/latest/api/http/index/Response-class.html