Example of Http Interceptor for login authentication

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An Http Interceptor can be used to verify if the user is logged in or to inject http headers to every http request.

In the example above, we are injecting a Authorization http header to every request:

auth-interceptor.js

import { Injectable, Injector } from '@angular/core';
import { HttpInterceptor, HttpRequest, HttpHandler, HttpEvent } from '@angular/common/http';
import { Observable } from 'rxjs/Observable';
import { LoginService } from './login.service';
 
@Injectable()
export class AuthInterceptor implements HttpInterceptor {
 
  constructor(private injector: Injector) {
 
  }
 
  intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    const loginService = this.injector.get(LoginService);
 
    if (loginService.isLoggedIn()) {
      const authRequest = request.clone(
        { setHeaders:{'Authorization': `Bearer ${loginService.getUser().accessToken}`}});
 
      return next.handle(authRequest);
    } else {
      return next.handle(request);
    }
  }
}

In your module:

import { HTTP_INTERCEPTORS, HttpClientModule } from '@angular/common/http';
import { AuthInterceptor } from "./login/auth.interceptor";
 
@NgModule({
  ...
  providers: [
    ...
    {
      provide: HTTP_INTERCEPTORS,
      useClass: AuthInterceptor,
      multi: true
    },
    ...
  ]
  ...
})