[login] Angular redirect to login page

I come from the Asp.Net MVC world where users trying to access a page they are not authorized are automatically redirected to the login page.

I am trying to reproduce this behavior on Angular. I came accross the @CanActivate decorator, but it results in the component not rendering at all, no redirection.

My question is the following:

• Does Angular provide a way to achieve this behaviour?
• If so, how? Is it a good practice?
• If not, what would be the best practice for handling user authorization in Angular?

Following the awesome answers above I would also like to CanActivateChild: guarding child routes. It can be used to add guard to children routes helpful for cases like ACLs

It goes like this

src/app/auth-guard.service.ts (excerpt)

import { Injectable }       from '@angular/core';
import {
  CanActivate, Router,
  ActivatedRouteSnapshot,
  RouterStateSnapshot,
  CanActivateChild
}                           from '@angular/router';
import { AuthService }      from './auth.service';

@Injectable()
export class AuthGuard implements CanActivate, CanActivateChild {
  constructor(private authService: AuthService, private router:     Router) {}

  canActivate(route: ActivatedRouteSnapshot, state:    RouterStateSnapshot): boolean {
    let url: string = state.url;
    return this.checkLogin(url);
  }

  canActivateChild(route: ActivatedRouteSnapshot, state:  RouterStateSnapshot): boolean {
    return this.canActivate(route, state);
  }

/* . . . */
}

src/app/admin/admin-routing.module.ts (excerpt)

const adminRoutes: Routes = [
  {
    path: 'admin',
    component: AdminComponent,
    canActivate: [AuthGuard],
    children: [
      {
        path: '',
        canActivateChild: [AuthGuard],
        children: [
          { path: 'crises', component: ManageCrisesComponent },
          { path: 'heroes', component: ManageHeroesComponent },
          { path: '', component: AdminDashboardComponent }
        ]
      }
    ]
  }
];

@NgModule({
  imports: [
    RouterModule.forChild(adminRoutes)
  ],
  exports: [
    RouterModule
  ]
})
export class AdminRoutingModule {}

This is taken from https://angular.io/docs/ts/latest/guide/router.html#!#can-activate-guard

Usage with the final router

With the introduction of the new router it became easier to guard the routes. You must define a guard, which acts as a service, and add it to the route.

import { Injectable } from '@angular/core';
import { CanActivate } from '@angular/router';
import { UserService } from '../../auth';

@Injectable()
export class LoggedInGuard implements CanActivate {
  constructor(user: UserService) {
    this._user = user;
  }

  canActivate() {
    return this._user.isLoggedIn();
  }
}

Now pass the LoggedInGuard to the route and also add it to the providers array of the module.

import { LoginComponent } from './components/login.component';
import { HomeComponent } from './components/home.component';
import { LoggedInGuard } from './guards/loggedin.guard';

const routes = [
    { path: '', component: HomeComponent, canActivate: [LoggedInGuard] },
    { path: 'login', component: LoginComponent },
];

The module declaration:

@NgModule({
  declarations: [AppComponent, HomeComponent, LoginComponent]
  imports: [HttpModule, BrowserModule, RouterModule.forRoot(routes)],
  providers: [UserService, LoggedInGuard],
  bootstrap: [AppComponent]
})
class AppModule {}

Detailed blog post about how it works with the final release: https://medium.com/@blacksonic86/angular-2-authentication-revisited-611bf7373bf9

Usage with the deprecated router

A more robust solution is to extend the RouterOutlet and when activating a route check if the user is logged in. This way you don't have to copy and paste your directive to every component. Plus redirecting based on a subcomponent can be misleading.

@Directive({
  selector: 'router-outlet'
})
export class LoggedInRouterOutlet extends RouterOutlet {
  publicRoutes: Array;
  private parentRouter: Router;
  private userService: UserService;

  constructor(
    _elementRef: ElementRef, _loader: DynamicComponentLoader,
    _parentRouter: Router, @Attribute('name') nameAttr: string,
    userService: UserService
  ) {
    super(_elementRef, _loader, _parentRouter, nameAttr);

    this.parentRouter = _parentRouter;
    this.userService = userService;
    this.publicRoutes = [
      '', 'login', 'signup'
    ];
  }

  activate(instruction: ComponentInstruction) {
    if (this._canActivate(instruction.urlPath)) {
      return super.activate(instruction);
    }

    this.parentRouter.navigate(['Login']);
  }

  _canActivate(url) {
    return this.publicRoutes.indexOf(url) !== -1 || this.userService.isLoggedIn()
  }
}

The UserService stands for the place where your business logic resides whether the user is logged in or not. You can add it easily with DI in the constructor.

When the user navigates to a new url on your website, the activate method is called with the current Instruction. From it you can grab the url and decide whether it is allowed or not. If not just redirect to the login page.

One last thing remain to make it work, is to pass it to our main component instead of the built in one.

@Component({
  selector: 'app',
  directives: [LoggedInRouterOutlet],
  template: template
})
@RouteConfig(...)
export class AppComponent { }

This solution can not be used with the @CanActive lifecycle decorator, because if the function passed to it resolves false, the activate method of the RouterOutlet won't be called.

Also wrote a detailed blog post about it: https://medium.com/@blacksonic86/authentication-in-angular-2-958052c64492

1. Create a guard as seen below. 2. Install ngx-cookie-service to get cookies returned by external SSO. 3. Create ssoPath in environment.ts (SSO Login redirection). 4. Get the state.url and use encodeURIComponent.

import { Injectable } from '@angular/core';
import { CanActivate, Router, ActivatedRouteSnapshot, RouterStateSnapshot } from 
  '@angular/router';
import { CookieService } from 'ngx-cookie-service';
import { environment } from '../../../environments/environment.prod';

@Injectable()
export class AuthGuardService implements CanActivate {
  private returnUrl: string;
  constructor(private _router: Router, private cookie: CookieService) {}

canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot): boolean {
    if (this.cookie.get('MasterSignOn')) {
      return true;
    } else {
      let uri = window.location.origin + '/#' + state.url;
      this.returnUrl = encodeURIComponent(uri);      
      window.location.href = environment.ssoPath +  this.returnUrl ;   
      return false;      
    }
  }
}

Please, do not override Router Outlet! It's a nightmare with latest router release (3.0 beta).

Instead use the interfaces CanActivate and CanDeactivate and set the class as canActivate / canDeactivate in your route definition.

Like that:

{ path: '', component: Component, canActivate: [AuthGuard] },

Class:

@Injectable()
export class AuthGuard implements CanActivate {

    constructor(protected router: Router, protected authService: AuthService)
    {

    }

    canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot): Observable<boolean> | boolean {

        if (state.url !== '/login' && !this.authService.isAuthenticated()) {
            this.router.navigate(['/login']);
            return false;
        }

        return true;
    }
}

See also: https://angular.io/docs/ts/latest/guide/router.html#!#can-activate-guard

Here's an updated example using Angular 4 (also compatible with Angular 5 - 8)

Routes with home route protected by AuthGuard

import { Routes, RouterModule } from '@angular/router';

import { LoginComponent } from './login/index';
import { HomeComponent } from './home/index';
import { AuthGuard } from './_guards/index';

const appRoutes: Routes = [
    { path: 'login', component: LoginComponent },

    // home route protected by auth guard
    { path: '', component: HomeComponent, canActivate: [AuthGuard] },

    // otherwise redirect to home
    { path: '**', redirectTo: '' }
];

export const routing = RouterModule.forRoot(appRoutes);

AuthGuard redirects to login page if user isn't logged in

Updated to pass original url in query params to login page

import { Injectable } from '@angular/core';
import { Router, CanActivate, ActivatedRouteSnapshot, RouterStateSnapshot } from '@angular/router';

@Injectable()
export class AuthGuard implements CanActivate {

    constructor(private router: Router) { }

    canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot) {
        if (localStorage.getItem('currentUser')) {
            // logged in so return true
            return true;
        }

        // not logged in so redirect to login page with the return url
        this.router.navigate(['/login'], { queryParams: { returnUrl: state.url }});
        return false;
    }
}

For the full example and working demo you can check out this post

Refer this code, auth.ts file

import { CanActivate } from '@angular/router';
import { Injectable } from '@angular/core';
import {  } from 'angular-2-local-storage';
import { Router } from '@angular/router';

@Injectable()
export class AuthGuard implements CanActivate {
constructor(public localStorageService:LocalStorageService, private router: Router){}
canActivate() {
// Imaginary method that is supposed to validate an auth token
// and return a boolean
var logInStatus         =   this.localStorageService.get('logInStatus');
if(logInStatus == 1){
    console.log('****** log in status 1*****')
    return true;
}else{
    console.log('****** log in status not 1 *****')
    this.router.navigate(['/']);
    return false;
}


}

}
// *****And the app.routes.ts file is as follow ******//
      import {  Routes  } from '@angular/router';
      import {  HomePageComponent   } from './home-page/home- page.component';
      import {  WatchComponent  } from './watch/watch.component';
      import {  TeachersPageComponent   } from './teachers-page/teachers-page.component';
      import {  UserDashboardComponent  } from './user-dashboard/user- dashboard.component';
      import {  FormOneComponent    } from './form-one/form-one.component';
      import {  FormTwoComponent    } from './form-two/form-two.component';
      import {  AuthGuard   } from './authguard';
      import {  LoginDetailsComponent } from './login-details/login-details.component';
      import {  TransactionResolver } from './trans.resolver'
      export const routes:Routes    =   [
    { path:'',              component:HomePageComponent                                                 },
    { path:'watch',         component:WatchComponent                                                },
    { path:'teachers',      component:TeachersPageComponent                                         },
    { path:'dashboard',     component:UserDashboardComponent,       canActivate: [AuthGuard],   resolve: { dashboardData:TransactionResolver } },
    { path:'formone',       component:FormOneComponent,                 canActivate: [AuthGuard],   resolve: { dashboardData:TransactionResolver } },
    { path:'formtwo',       component:FormTwoComponent,                 canActivate: [AuthGuard],   resolve: { dashboardData:TransactionResolver } },
    { path:'login-details', component:LoginDetailsComponent,            canActivate: [AuthGuard]    },

];