multiple database with --pw-stdin (#2916)

* Updated utilities to unlock KDBX with OS password manager on macOS and Linux
* Use a static stream on stdin for --pw-stdin otherwise buffer loss eliminates subsequent passwords
* Update INSTALL requirements

utils/keepassxc-kdewallet

@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+# fetch KeePass database passwords from kdewallet
+
+### change the path to suit your installation or set KDBX_SEARCH before calling ###
+: ${KDBX_SEARCH:=~/.KeePass/*.kdbx}
+
+PROG="${0##*/}"
+KEEPASSXC=$(which -a keepassxc | sed -e "\\,$0,d" -e 'q')
+
+function daemon_main {
+  # open kdewallet
+  handle=$(qdbus org.kde.kwalletd5 /modules/kwalletd5 org.kde.KWallet.open kdewallet 0 "$PROG")
+  while [[ true != $(qdbus org.kde.kwalletd5 /modules/kwalletd5 org.kde.KWallet.isOpen kdewallet) ]]; do
+    sleep 1
+  done
+
+  declare -A DBs
+  for DBPATH in $(ls -r $KDBX_SEARCH); do
+    DBs[$(realpath $DBPATH)]=$(qdbus org.kde.kwalletd5 /modules/kwalletd5 org.kde.KWallet.readPassword "$handle" "Passwords" "${DBPATH##*/}" "$PROG")
+  done
+
+  # launch real keepassxc
+  IFS=$'\n\n\n'
+  "$KEEPASSXC" --pw-stdin "${!DBs[@]}" <<<"${DBs[*]}" &
+
+  # done with kdewallet
+  qdbus org.kde.kwalletd5 /modules/kwalletd5 org.kde.KWallet.close "$handle" "false" "$PROG"
+}
+
+if [[ '-d' = "$1" ]]; then
+  exec >&~/tmp/$PROG.log
+  set -vx
+  daemon_main
+else
+  cd /
+  daemon_main </dev/null >&/dev/null &
+  disown
+fi