This functionality is already in the product.
GAD has Resource connections for GHTTPS servers. This allows you to connect to the GAS Server just for this type of Secure Mail Transfer.
In basic terms, you could have a GAD workflow (Called by a Monitor, Scheduled job, External API Call, etc) executed that Reads data from a DB Table, then sends a Secure Mail link out (through GAS) to the email associated to the record read from the table. Then, attach any document to that and send it just like you would if you were sitting in front of a screen.
Any of this can be automated between GAD and GAS.
And, the newer versions (5.0+) combine the GAS and GAD features into a single user interface. Allowing for this to happen within the same server, instead of separated connections.
Check out the Release Notes