title: ajax post request - cross-Origin Read Blocking (CORB) blocked cross-origin response CORS
body: <p>I have a jquery frontend project which sends POST request to my ASMX Webservice (c#) with ajax. Everything works fine, instead of one special request. </p>
  
  <p>The application is something like a shopping app. The Post-request which sends the order to the database works well if i have less than 5 items in the cart. If I have 5 items or more I get a CORS-Error. </p>
  
  <p>My Backend (on IIS) has the following configuration: </p>
  
  <pre><code> &lt;httpProtocol&gt;
        &lt;customHeaders&gt;
          &lt;add name="Access-Control-Allow-Origin" value="*" /&gt;
          &lt;add name="Access-Control-Allow-Methods" value="POST" /&gt;
          &lt;add name="Access-Control-Allow-Headers" value="Accept,Authorization,Cache-Control,Content-Type,DNT,If-Modified-Since,Keep-Alive,Origin,User-Agent,X-Requested-With" /&gt;
  
        &lt;/customHeaders&gt;
      &lt;/httpProtocol&gt;
  </code></pre>
  
  <p>This is a Simple CORS request (only POST is allowed) to avoid OPTIONS pre-flight request. The OPTIONS request gives me also an CORS- error with 404. 
  Without the OPTIONS and only with POST i get this error: </p>
  
  <blockquote>
  <pre><code>    POST https://sperrmuellportalapi.ks-weimar.de/webservice_ex.asmx/SP_WRITE_Sperrmuellanmeldung
  </code></pre>
    
    <p>403 (Forbidden)
        send @ jquery-3.1.1.min.js:4
        ajax @ jquery-3.1.1.min.js:4
        SPWriteSperrmuellanmeldung @ index.js:3469
        (anonymous) @ index.js:3380
        dispatch @ jquery-3.1.1.min.js:3
        q.handle @ jquery-3.1.1.min.js:3</p>
  
  <pre><code>/#zsfg_sp_anmelden:1 Failed to load https://sperrmuellportalapi.ks-weimar.de/webservice_ex.asmx/SP_WRITE_Sperrmuellanmeldung:
  </code></pre>
    
    <p>No 'Access-Control-Allow-Origin' header is present on the requested
    resource. Origin '<a href="https://sperrmuellportal.ks-weimar.de" rel="nofollow noreferrer">https://sperrmuellportal.ks-weimar.de</a>' is therefore
    not allowed access. The response had HTTP status code 403.</p>
  
  <pre><code>jquery-3.1.1.min.js:4 Cross-Origin Read Blocking (CORB) blocked cross-origin response
  </code></pre>
    
    <p><a href="https://sperrmuellportalapi.ks-weimar.de/webservice_ex.asmx/SP_WRITE_Sperrmuellanmeldung" rel="nofollow noreferrer">https://sperrmuellportalapi.ks-weimar.de/webservice_ex.asmx/SP_WRITE_Sperrmuellanmeldung</a>
    with MIME type text/html. See
    <a href="https://www.chromestatus.com/feature/5629709824032768" rel="nofollow noreferrer">https://www.chromestatus.com/feature/5629709824032768</a> for more
    details.</p>
  </blockquote>
  
  <p>The ajax request starts like this: </p>
  
  <pre><code>$.ajax({
          type: "POST",
          dataType: "xml",
          url: UrlToWebservice + "SP_WRITE_Sperrmuellanmeldung",
  
          data: {..some params..}, ...
  </code></pre>
  
  <p>It is an ASMX Webservice, so I use XML as exchange format.</p>
  
  <p>This question is related to this one: <a href="https://stackoverflow.com/questions/51825920/ajax-post-the-response-had-http-status-code-403-headers-are-missing-always-o">ajax POST - The response had HTTP status code 403, headers are missing, always OPTIONS</a></p>
  
  <p>I am so clueless, I'm looking for a solution for days now. Please help. :( </p>