This article discusses the Google requirements of using Google Drive through a proxy server.
Applies to the following Sophos products
Sophos Web Appliance
What To Do
Google Drive can work though a proxy server (such as the Sophos UTM, or Sophos Web Appliance), but Google does not support authentication for connections to their addresses. To allow Google Drive to work though your proxy, you must bypass authentication for the addresses contained in the Google article below.
As Google does not support NTLM or Kerberos authentication with Google Drive you will not be able to set user based rules for access the system. It is however possible to configure these rules by IP address on the Sophos Web Appliance.
On the Sophos UTM, you can add an exception in WebAdmin under Web Protection > Filtering Options > Exceptions. You'll want to ensure 'Authentication' is checked under 'Skip these checks', and the list of domains in the Google KB above is added into the 'Target Domains' list after selecting For All Requests > Matching these URLs.
If you are unable to use Google Drive after bypassing authentication for these domains, please contact Sophos Technical Support: