How to get Request Header value when accessing my Angular application

because there is no method to do this. Your Application is running in the browser, so your application doesnt receive any requests, but the browser does. You should probably find another architecture. Involve your backend in the flow. Maybe construct an endpoint which is redirecting to your application.

Another same question

So the only way I know to retrieve anything from the headers is the httpInterceptor, that is intercepting any outgoing request and is observing the response like so:

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

@Injectable()
export class HeaderInterceptor implements HttpInterceptor {

   constructor(private userService: UserService, 
               private constantsService: ConstantsService){ }

public intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {

    if(req.url.includes(/*whatever you are looking for*/)) { 

    }

    return next.handle(req).do((suc) => {
        if(suc.type !== 0){
            const whateverDataYouNeed = suc['headers'].get(/*whatever header you need*/);
            // Do something with it           
        }

    }).
    catch((error, caught) => {
        return Observable.throw(error);
    }) as any;
  }
}

Best regards!