How to redirect to logout when token expired in angular 4

Question

I have a angular 4 application. There i use JWT token for authentication purposes. Everything works fine. but the token expiration time i have given to the JWT token is 1 hour. i want to log the user out from the front end application once the token expired on the server-side. in node backend, i use express middleware to handle this by checking if all the requests contain a valid token. Is there a way to do this angular side as well?

Answer 1

You can use Http Interceptors. If any Unauthorized 401 response. Suppose you are sending a http request with token in header. your server side code check your token and finally find out, token is invalid/expire return 401 code and you can redirect the user to login page. and manually passing token and checking all http request authorized/unauthorized is very repeated work, this common task you can do by interceptors as delegate for http request. see the code samples you'll get your solution.

AppHttpInterceptor.ts

import { Injectable } from "@angular/core";
import {
    HttpInterceptor,
    HttpRequest,
    HttpResponse,
    HttpErrorResponse,
    HttpHandler,
    HttpEvent
} from '@angular/common/http';

import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/do';
import 'rxjs/add/operator/catch';
import 'rxjs/add/observable/throw';
import { Http, Response, RequestOptions, Headers } from '@angular/http';
import { Router } from '@angular/router'


@Injectable()
export class AppHttpInterceptor implements HttpInterceptor {
    constructor(private router: Router){

    }
    headers = new Headers({
        'Content-Type': 'application/json',
        'Token': localStorage.getItem("Token")
    });
    intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {

        console.log("intercepted request ... ");

        // Clone the request to add the new header.
        const authReq = req.clone({ headers: req.headers.set("Token", localStorage.getItem("Token")) });

        console.log("Sending request with new header now ...");

        //send the newly created request
        return next.handle(authReq)
            .catch(err => {
                // onError
                console.log(err);
                if (err instanceof HttpErrorResponse) {
                    console.log(err.status);
                    console.log(err.statusText);
                    if (err.status === 401) {
                        window.location.href = "/login";
                    }
                }
                return Observable.throw(err);
            }) as any;
    }
}

app.module.ts

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { HttpModule } from '@angular/http';
import { HttpClient } from "@angular/common/http";
import { FormsModule } from '@angular/forms';
import { ToasterModule, ToasterService } from "angular2-toaster";
import { BrowserAnimationsModule } from '@angular/platform-browser /animations';
import { RouterModule } from '@angular/router';
import { ReactiveFormsModule } from '@angular/forms';
import { HttpClientModule,HTTP_INTERCEPTORS} from '@angular/common/http';
import {AppHttpInterceptor} from './Common/AuthInterceptor';
import { AppRoutes } from '../app/Common/Routes';
import { AppComponent } from './app.component';

@NgModule({
  declarations: [
    AppComponent,
  ],
  imports: [
    BrowserModule, HttpModule,HttpClientModule, ReactiveFormsModule, FormsModule, BrowserAnimationsModule, RouterModule.forRoot(AppRoutes)
  ],
 providers: [
 {
   provide: HTTP_INTERCEPTORS,
   useClass: AppHttpInterceptor,
   multi: true
 }
],
bootstrap: [AppComponent]
})
export class AppModule { 
  constructor(private httpClient: HttpClient){
    this.httpClient.get("https://jsonplaceholder.typicode.com/users").subscribe(
  success => {
    console.log("Successfully Completed");
    console.log(success);
  }
  );
 }

}

Answer 2

you can check if the token is expired or not and as a response, you can redirect to login page store token in local storage for example

 yourmthod(parametr) {
        this.token = localStorage.getItem("token");
        this.headers = new Headers();
        this.headers.delete(this.token);
        this.headers.append("Authorization", this.token);
        return this._http.post(Constants.SERVER_URL + 'your method', {headers: this.headers});
    }

so it will response 401 error and you can handle this by redirecting to your login page

if any query you can ask a question in comments so I can help you

and you can also use if-else in your method

and you can write code in app.component.ts in onIt() method

ngOnInit(): void {
        let token = localStorage.getItem("token");
        if (token) {
            this.isTokenAvaialable = true;
            this.http.get(Constants.SERVER_URL + 'your mthod to validate token' + token).subscribe(data => {
                if (data == true) {
                    if (window.location.pathname == "") {
                        this.router.navigate(['/home', {outlets: {'r2': ['dashboard']}}]);
                    }
                } else if (data == false) {

                    this.logout('Server restarted.Please login again!!');
                } else {

                    this.logout('Session expired.Please login again.!!');
                }

            }, (err: HttpErrorResponse) => {
                this.toastr.warning('Server restarted.Please login again!!', 'Alert');
                localStorage.removeItem("token");
                this.isTokenAvaialable = false;
                this.logout('Server restarted.Please login again!!');
            });
        } else {
            this.isTokenAvaialable = false;
            this.router.navigate(['']);
            localStorage.removeItem("token");
            this.isTokenAvaialable = false;
        }
    }