Daiki Ueno <ueno@unixuser.org> writes:

> If you want to simply skip the key selection, I'd suggest to do:
>
> (make-local-variable 'epa-file-encrypt-to)
> (setq epa-file-encrypt-to nil)
>
> in the "authinfo.gpg" buffer (see epa-file-write-region).

Find below a proposed patch to auth-source.el.

BTW, I forgot to mention in the previous response, I think it overkill
to make epa-file to encrypt files with symmetric encryption by default,
because as long as a file is visited in a buffer, epa-file remembers the
last used encryption method (in epa-file-encrypt-to local variable),
which will be used on the next save-buffer.  So a user should see the
key selection UI only the first time she saves the buffer.

Default symmetric might be useful when Emacs does visit/save/kill-buffer
repeatedly, but I think it is a rare case.