interceptor.ts

import { Injectable } from '@angular/core';
import { HttpInterceptor, HttpRequest, HttpHandler, HttpEvent } from '@angular/common/http';
import { Observable } from 'rxjs';

@Injectable()
export class AuthInterceptor implements HttpInterceptor {

  constructor() { }

  intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    request = this.addToken(request);
    return next.handle(request);
  }

  private addToken(request: HttpRequest<any>) {
    const token = '123';
    if (true) {
      request = request.clone({
        setHeaders: {
          token,
        },
      });
      return request;
    }
    return request;
  }
}
//
providers: [
    {
      provide: HTTP_INTERCEPTORS,
      useClass: AuthInterceptor,
      multi: true
    }
  ],