start: forward SSH agent requests from WSL to Windows

Instruction that I followed:

    https://stuartleeks.com/posts/wsl-ssh-key-forward-to-windows/

Using this tool to make Windows named pipes available in WSL:

    https://github.com/jstarks/npiperelay

utils/bin/start

@@ -1,3 +1,49 @@
 #!/bin/sh
-exec ssh-agent tmux new-session -A -t main "$@"
+usage () {
+  echo "usage: $0 [-w] [-h]"
+  echo "   -w   use the WSL ssh-agent instead of OpenSSH for Windows"
+  echo "   -h   show help and exit"
+}
+
+# Use OpenSSH for Windows by default.
+WSL_SSH_AGENT=false
+
+while getopts ":wh" arg; do
+  case "$arg" in
+    w)
+      WSL_SSH_AGENT=true
+      ;;
+
+    h)
+      >&2 usage
+      exit 0
+      ;;
+
+    ?)
+      >&2 echo "ERROR: unknown option -$OPTARG"
+      >&2 usage
+      exit 1
+      ;;
+  esac
+done
+
+if [ "$WSL_SSH_AGENT" = true ]; then
+  exec ssh-agent tmux new-session -A -t main "$@"
+fi
+
+require() {
+  if ! command -v "$@" >/dev/null 2>&1; then
+    >&2 echo "ERROR: required command not found: $1"
+    exit 1
+  fi
+}
+
+require socat
+require npiperelay
+
+# Forward SSH Agent requests from withitn WSL to OpenSSH for Windows, based on:
+# https://stuartleeks.com/posts/wsl-ssh-key-forward-to-windows/
+export SSH_AUTH_SOCK=$HOME/.ssh/agent.sock
+socat UNIX-LISTEN:$SSH_AUTH_SOCK,fork EXEC:"npiperelay -ei -s //./pipe/openssh-ssh-agent",nofork &
+exec tmux new-session -A -t main "$@"