I have googled Desired State Configuration and checked the Microsoft site for information on specifying settings for IIS servers, specifically using DSC to make IIS servers STIG compliant. Unfortunately, I can't find many details specifically for IIS web server setting. Any recommendations or code examples would be greatly appreciated.
To set the Custom Logging Fields name in iis you could use the below PowerShell command:
New-ItemProperty 'IIS:\Sites\Default Web Site' -Name logfile.customFields.collection -Value @{logFieldName='testname';sourceType='RequestHeader';sourceName='c-ip'}