I use a Yubikey to store a GPG key pair and I like to use this key pair as my SSH key too. GPG on Windows exposes a Pageant style SSH agent and I wanted a way to use this key within WSL2.

1. Run sudo apt-get install socat
2. Download latest version from release page and copy wsl2-ssh-pageant.exe to your $HOME/.ssh directory
3. Set the executable bit on wsl2-ssh-pageant.exe: chmod +x $HOME/.ssh/wsl2-ssh-pageant.exe
4. (a) Add the following to your .bashrc or .zshrc (for bash/zsh shell):

export SSH_AUTH_SOCK=$HOME/.ssh/agent.sock
ss -a | grep -q $SSH_AUTH_SOCK
if [ $? -ne 0 ]; then
        rm -f $SSH_AUTH_SOCK
        (setsid nohup socat UNIX-LISTEN:$SSH_AUTH_SOCK,fork EXEC:$HOME/.ssh/wsl2-ssh-pageant.exe >/dev/null 2>&1 &)
fi

export GPG_AGENT_SOCK=$HOME/.gnupg/S.gpg-agent
ss -a | grep -q $GPG_AGENT_SOCK
if [ $? -ne 0 ]; then
        rm -rf $GPG_AGENT_SOCK
        (setsid nohup socat UNIX-LISTEN:$GPG_AGENT_SOCK,fork EXEC:"$HOME/.ssh/wsl2-ssh-pageant.exe --gpg S.gpg-agent" >/dev/null 2>&1 &)
fi

4. (b) Add the following to your config.fish (for fish shell):

set -x SSH_AUTH_SOCK $HOME/.ssh/agent.sock
ss -a | grep -q $SSH_AUTH_SOCK
if [ $status != 0 ]
  rm -f $SSH_AUTH_SOCK
  setsid nohup socat UNIX-LISTEN:$SSH_AUTH_SOCK,fork EXEC:$HOME/.ssh/wsl2-ssh-pageant.exe >/dev/null 2>&1 &
end

set -x GPG_AGENT_SOCK $HOME/.gnupg/S.gpg-agent
ss -a | grep -q $GPG_AGENT_SOCK
if [ $status != 0 ]
  rm -rf $GPG_AGENT_SOCK
  setsid nohup socat UNIX-LISTEN:$GPG_AGENT_SOCK,fork EXEC:"$HOME/.ssh/wsl2-ssh-pageant.exe --gpg S.gpg-agent" >/dev/null 2>&1 &
end

Some of the code is copied from benpye's wsl-ssh-pageant. This code shows how to communicate to pageant.