Question: I am stuck in a issue that happens when user manually changes the route in browser tab and presses enter. This forces my ui-router/angular2-router to navigate to the state entered by user. I want to prevent this and allow routing only through the flow I have implemented by button clicks in my website.

Answer: 
Its 2018! Angular 5 is here and so is the solution to this issue. BAMM its **CanActivate** Interface that a class can implement to be a guard deciding if a route can be activated.

We can add this functionality and prevent the access to some of our routes based on the conditions we define. A service for eg AuthGuard that implements the CanActivate interface and defines the canActivate method can be added to route configuration.

```
class Permissions {
  canGoToRoute(user: UserToken, id: string): boolean {
    return true;
  }
}

@Injectable()
class AuthGuard implements CanActivate {
  constructor(private permissions: Permissions, private currentUser: UserToken) {}

  canActivate(
    route: ActivatedRouteSnapshot,
    state: RouterStateSnapshot
  ): Observable<boolean>|Promise<boolean>|boolean {
    return this.permissions.canGoToRoute(this.currentUser, route.params.id);
  }
}

```

If we have a route that we want to protect access to against some condition, we add the guard as follows:

```
const appRoutes: Routes = [
  { path: 'crisis-center', component: CrisisListComponent },
  {
    path: 'heroes',
    canActivate: [AuthGuard],
    component: HeroListComponent,
    data: { title: 'Heroes List' }
  },
  { path: '',
    redirectTo: '/heroes',
    pathMatch: 'full'
  },
  { path: '**', component: PageNotFoundComponent }
];

```

Here the route `heroes` and all its children have a layer of guard over it. Hence based on the boolean value returned by the AuthGuard service the user will be allowed or denied access to this route.
You can import router in the constructor of a guard. This router instance will have the current URL. ActivatedRouteSnapshot and RouterStateSnapshot in canActivate will contain the URL that the user is attempting to access.

The below example prevents users from directly accessing a route from an outside page.

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

@Injectable()
export class DirectAccessGuard implements CanActivate {
  constructor(private router: Router) {}

  canActivate(
    next: ActivatedRouteSnapshot,
    state: RouterStateSnapshot): Observable<boolean> | Promise<boolean> | boolean {
    // If the previous URL was blank, then the user is directly accessing this page
    if (this.router.url === '/') {
      this.router.navigate(['']); // Navigate away to some other page
      return false;
    }
    return true;
  }
}

```

Add this guard to your routing module

```
{ path: 'signup/:type/:step', component: SignupComponent, canActivate: [DirectAccessGuard] }

```