auth-source-netrc-use-gpg-tokens is a variable defined in `auth-source.el'.
Its value is

Set this to tell auth-source when to create GPG password
tokens in netrc files. It's either an alist or `never'.
Note that if EPA/EPG is not available, this should NOT be used.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 23.2 of Emacs.