Hello,

For this purpose you can create a custom Global event which will be using DocumentEvents.Insert.After (see an example in the Dev Guide) and here you can simply set this property for every document immediately after it is created.

There is a field/column for this purpose in CMS_Tree table in database: RequiresSSL.

You can set these field using the standard approach with node.SetValue() method:
API Examples - Creating documents

Options for Requires SSL:

Yes => RequiresSSL = 1
No => RequiresSSL = 0
Inherits => RequiresSSL = NULL
Never => RequiresSSL = 2

Best Regards,
Martin Danko