ASP.Net IIS web application send all requests via proxy without code change

For your web application, edit the web.config file (in the app root) and add as shown below. Note: you may already have a system.net or configuration section. You will have to add the defaultproxy section to the existing parent elements as needed

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <system.net>
    <defaultProxy enabled="true" useDefaultCredentials="true">
      <proxy proxyaddress="http://proxyservername:proxyserverport/" bypassonlocal="false" usesystemdefault="false" autoDetect="false" />
    </defaultProxy>
  </system.net>
</configuration>