src/app/auth/auth.interceptor.ts

import { Injectable } from '@angular/core';
import { HttpEvent, HttpHandler, HttpInterceptor, HttpRequest, HttpErrorResponse } from '@angular/common/http';
import { Observable, throwError } from 'rxjs';
import { AuthService } from './auth.service';
import { catchError } from 'rxjs/operators';
import { AuthUiService } from './auth-ui.service';

@Injectable()
export class AuthInterceptor implements HttpInterceptor {
  constructor(
    private auth: AuthService,
    private authUi: AuthUiService
  ) {}

  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    const token = this.auth.getAccessToken();

    let authReq = req;
    if (token && !req.headers.has('Authorization')) {
      authReq = req.clone({
        setHeaders: { Authorization: `Bearer ${token}` }
      });
    }

    return next.handle(authReq).pipe(
      catchError((err: HttpErrorResponse) => {
        if (err.status === 401) {
          this.auth.logout();
          this.authUi.openSignin();
        }
        return throwError(() => err);
      })
    );
  }
}