For this to work, the ProxySG must have SSL Interception enabled and configured, and the ProxySG must be able to see the full URL path for the HTTPS request.
If you haven't configured SSL Interception please follow TECH244873
 
The following URL is the one used in this example:
https://docs.google.com/spreadsheets/d/<string>/edit#gid=0

 
Once you have configured the ProxySG for SSL Interception, you will need to add a new Web Access Layer:


In the image above the new Web Access Layer is called Google Docs.

First, add a rule to allow access to the URL that the users need to access. However due to how Google maintains the URLs for the docs, you cannot just copy the whole URL; you have to make use of regular expression to validate the URL path. For our example URL, we will use this part of the URL:

/spreadsheets/d/<string>

Third, add a rule to allow the HTTP/HTTPS CONNECT method.

 
Forth, add a rule that blocks access to https://docs.google.com:

The rules will look like the one below.

With these four rules, users will now have access to the Doc that is required but access to docs.google.com will be blocked and you will not be able to access any other docs hosted by docs.google.com.