etc/X11/Xsession.d/35x11-common_xhost-local

# This file is sourced by Xsession(5), not executed.

# If xhost (from x11-xserver-utils) is installed, use it to give access 
# to the X server to any process from the same user on the local host.
# Unlike other uses of xhost, this is safe since the kernel can check 
# the actual owner of the calling process.

if type xhost >/dev/null 2>&1; then
  xhost +si:localuser:$(id -un) || :
fi