I have a use case where gpg needs to work non-interactively with a
smartcard (here, a YubiKey).

According to the docs [1], it is possible to seed gpg-agent with
passphrases, using the gpg-preset-passphrase utility.

This requires starting gpg-agent with --allow-preset-passphrase,
which I have done.

However, no matter what I do, I still always get a PIN request.


Steps to reproduce:

1. Add allow-preset-passphrase to $GNUPGHOME/gpg-agent.conf
2. Reload the agent
3. Get the relevant keygrip (here, for a [S]igning subkey):

   $ KEYGRIP="$(gpg --list-secret-keys --with-keygrip | \
	grep -A 1 '\[S\]' | \
	sed -nr 's/.*Keygrip = ([A-F0-9]+)/\1/p')"

4. Seed the agent:

   $ echo "MY_PASSWORD" | \
	/usr/lib/gnupg/gpg-preset-passphrase --preset "$GPG_KEYGRIP"

5. Try signing something:

   $ gpg --sign --output /dev/null /dev/null

And the PIN dialog still always appears.

I think I've tried all variations of this: preseeding all available
keygrips with the password (in case I got the wrong one), using FPRs,
using echo -n, etc.

From the various examples I can find on the net, I do feel like I'm
doing everything right.

Best,
Christian


[1]: https://www.gnupg.org/documentation/manuals/gnupg/gpg_002dpreset_002dpassphrase.html