title: How to change parameter in Observable (RxJs)
body: <p>I use HTTP provider in Angular 2 for data loading from API.</p>
  
  <pre><code>return this.http.post(url, urlSearchParams.toString(), {
          headers: this.getHttpHeaders()
      })
      .retryWhen((error) =&gt; {
          return this.handleRetryError(error);
      })
  </code></pre>
  
  <p>When there is no or old session I create new one in this.handleRetryError(error) and fill headers with it. (method getHttpHeaders() returns array with headers)</p>
  
  <p>RetryWhen tries to do this post again, but there is unchanged (old) headers from first round.</p>
  
  <p><strong>Is there any chance to change headers parameter for http.post from .readyWhen?</strong></p>
  
  <p>Thank you very much for help :)</p>