How to set headers and body for SPFx httpClient

SPFxhttpClientExample.ts

import { HttpClient, IHttpClientOptions, HttpClientResponse } from '@microsoft/sp-http';

private makeRequest(value1: string, value2: string, value3: string): Promise<HttpClientResponse> {

  const postURL = "https://REST-API-URL";

  const body: string = JSON.stringify({
    'name1': value1,
    'name2': value2,
    'name3': value3,
  });

  const requestHeaders: Headers = new Headers();
  requestHeaders.append('Content-type', 'application/json');
  requestHeaders.append('Cache-Control', 'no-cache');
  //For an OAuth token
  requestHeaders.append('Authorization', 'Bearer <TOKEN>');
  //For Basic authentication
  requestHeaders.append('Authorization', 'Basic <CREDENTIALS>');

  const httpClientOptions: IHttpClientOptions = {
    body: body,
    headers: requestHeaders
  };

  console.log("About to make REST API request.");

  return this.context.httpClient.post(
    postURL,
    HttpClient.configurations.v1,
    httpClientOptions)
    .then((response: Response): Promise<HttpClientResponse> => {
      console.log("REST API response received.");
      return response.json();
    });
}

I am calling custom web service hosted into dedicated server through POST method from SPFx. I am fetching token from https://graph.windows.net and passing into header. But I am getting below error in POST method.
Access to fetch at 'https://MyServer/WebService.svc/PostMethod' from origin 'https://MYDOMAIN.sharepoint.com' has been blocked by CORS policy: Request header field cache-control is not allowed by Access-Control-Allow-Headers in preflight response.

@manjeetjagtap Check if you've enabled CORS on the AppService that is hosting your Web Service

You will likely need to setup some kind of proxy function if you're pulling your hair out trying to get it to work - here's a good article on the topic https://github.com/ravichandran-blog/SPFx/tree/master/spfx-cors