401 unauthorized requests now redirect users to the login page

src/app/http.interceptor.ts

@@ -0,0 +1,34 @@
+import { HttpEvent, HttpHandler, HttpInterceptor, HttpRequest } from '@angular/common/http';
+import { Injectable } from '@angular/core';
+import { MatSnackBar } from '@angular/material/snack-bar';
+import { Router } from '@angular/router';
+import { Observable, throwError } from 'rxjs';
+import { catchError } from 'rxjs/operators';
+
+@Injectable()
+export class H401Interceptor implements HttpInterceptor {
+
+    constructor(private router: Router, private snackBar: MatSnackBar) { }
+
+    intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
+        return next.handle(request).pipe(catchError(err => {
+            if (err.status === 401) {
+                localStorage.setItem('jwt_token', null);
+                if (this.router.url !== '/login') {
+                    this.router.navigate(['/login']).then(() => {
+                        this.openSnackBar('Login expired, please login again.');
+                    });
+                }
+            }
+
+            const error = err.error.message || err.statusText;
+            return throwError(error);
+        }));
+    }
+
+    public openSnackBar(message: string, action: string = '') {
+        this.snackBar.open(message, action, {
+          duration: 2000,
+        });
+      }
+}