auth.interceptor.ts

import {Injectable} from '@angular/core';
import {HttpEvent, HttpInterceptor, HttpHandler, HttpRequest} from '@angular/common/http';
 
@Injectable()
export class AuthInterceptor implements HttpInterceptor {
  constructor(private auth: AuthService) {}
 
  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    // Clone the request to add the new header.
    const authReq = req.clone({headers: req.headers.set('Authorization', 'my-token')});
    // Pass on the cloned request instead of the original request.
    return next.handle(authReq).do(
    (event: : HttpEvent<any>) => {
        if (event instanceof HttpResponse) {
         // Request successful : You can change response
        }
      }).catch(err => {
      if (err instanceof HttpErrorResponse {
          if (err.status === 403) {
            // Error Authorization
          }
        }
    });
  }
}