I have an IIS application that is querying Azure Active Directory Graph API from the server. I wanted to capture what is requests are happening using the client API. By default Fiddler does not capture these requests. Fiddler inserts itself into the WinINET layer as a proxy which is bypassed by IIS outgoing traffic.

To capture these requests  coming from an IIS application pool. Add to your web.config after the <configSections> element:

  <system.net>
    <defaultProxy enabled="true">
      <proxy proxyaddress="http://127.0.0.1:8888" bypassonlocal="False"/>
    </defaultProxy>
  </system.net>

where 8888 is the fiddler listening port, found in Tools > Fiddler Options

This can be found in the Fiddler documentation.

Happy web traffic debugging!