title: Setting requestTimeout in web.config of an ASP.NET Core Azure Web App via Application Settings
body: <p>I have a web.config that looks like so, and is added as a link to a number of applications in my solution:</p>
  
  <pre><code>&lt;configuration&gt;
    &lt;!-- For more info to customize the asp.net core module see https://go.microsoft.com/fwlink/?linkid=838655 --&gt;
    &lt;system.webServer&gt;
      &lt;!-- As connection proxy request contains double escape sequence, we need to enable it. background Azure ARM Apis are enabled it.  --&gt;
        &lt;security&gt;
        &lt;requestFiltering allowDoubleEscaping="true" /&gt;
      &lt;/security&gt;
      &lt;handlers&gt;
        &lt;add name="aspNetCore" path="*" verb="*" modules="AspNetCoreModule" resourceType="Unspecified"/&gt;
      &lt;/handlers&gt;
      &lt;aspNetCore processPath="%LAUNCHER_PATH%" arguments="%LAUNCHER_ARGS%" stdoutLogEnabled="false" stdoutLogFile="\\?\%home%\LogFiles\stdout"/&gt;
    &lt;/system.webServer&gt;
  &lt;/configuration&gt;
  </code></pre>
  
  <p>One of the services has potential for long running single requests, and so I want to increase the IIS request timeout for that service, which can be achieved by adding to the <code>aspNetCore</code> configuration like so:</p>
  
  <pre><code>&lt;aspNetCore processPath="%LAUNCHER_PATH%" arguments="%LAUNCHER_ARGS%" stdoutLogEnabled="false" stdoutLogFile="\\?\%home%\LogFiles\stdout" requestTimeout="00:10:00"/&gt;
  </code></pre>
  
  <p>However, given this web.config is otherwise shared and I don't want to alter the behaviour of my other apps, I'd like configure this via an application setting from my arm templates.</p>
  
  <p>When I attempt something like the following, I get an error that <code>%REQUEST_TIMEOUT%</code> is not a valid time, and deploying fails to startup the webapp. </p>
  
  <p>How can I enable app settings to insert into the request timeout field?</p>