title: ajax post request is No 'Access-Control-Allow-Origin' header is present on the requested resource.'
body: <p>I'm just making an ajax post request and I'm getting an error like:</p>
  
  <blockquote>
    <p>XMLHttpRequest cannot load https://xxx.com?redirect_uri=http://www.example.com. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://example.com' is therefore not allowed access.</p>
  </blockquote>
  
  <p>And here I can see there is nothing different from my response domain and request domain except "www", so does "www" also cause this issue?</p>