use windows pageant keys inside wsl2

pageant.bash

#!/bin/bash
# 
# use windows pageant keys inside wsl2
#
# call me from .bashrc on wsl

# on windows host:
#   shell:startup => "C:\Program Files\PuTTY\pageant.exe" --openssh-config %USERPROFILE%\.ssh\pageant.conf "C:\path\to\putty\key.ppk"
# 
#   %USERPROFILE%\.ssh\config contains all need hosts for ssh and vscode
#     Include pageant.conf
# 
#     Host alias
#       HostName ip-or-domain
#       User username
#     ...
# 
#   https://github.com/rupor-github/wsl-ssh-agent/releases/download/v1.6.9/wsl-ssh-agent.zip -> %USERPROFILE%/.local/bin/npiperelay.exe
# on wsl:
#   apt install wslu ; for wslvar

SSH_AUTH_SOCK="$HOME/.ssh/agent.sock"
# Exit if socket already exists and is a valid socket
if ss -a | grep -q "$SSH_AUTH_SOCK"; then
    return
fi

# Remove stale socket
rm -f "$SSH_AUTH_SOCK"

USER_PROFILE="$(wslpath $(wslvar USERPROFILE))"
PAGEANT_CONF="$USER_PROFILE/.ssh/pageant.conf"
NPIPERELAY="$USER_PROFILE/.local/bin/npiperelay.exe"
PAGEANT_PIPE=$(cat $PAGEANT_CONF | sed 1q | cut -d'"' -f2)

# copy config from windows host
cat $USER_PROFILE/.ssh/config \
    | sed "s#Include pageant.conf#IdentityAgent \"$SSH_AUTH_SOCK\"#" \
    > $HOME/.ssh/config

# Start socat/npiperelay as a background process
setsid socat \
    UNIX-LISTEN:"$SSH_AUTH_SOCK",unlink-close,unlink-early,fork \
    EXEC:"$NPIPERELAY -ei -s $PAGEANT_PIPE",nofork \
    >/dev/null 2>&1 &