/etc/ssh/sshrc to fix X11 Forwarding on Debian

sshrc

        if read proto cookie && [ -n "$DISPLAY" ]; then
                if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then
                        # X11UseLocalhost=yes
                        echo add unix:`echo $DISPLAY |
                            cut -c11-` $proto $cookie
                else
                        # X11UseLocalhost=no
                        echo add $DISPLAY $proto $cookie
                fi | xauth -q -
        fi

Warning: untrusted X11 forwarding setup failed: xauth key data not generated
X11 connection rejected because of wrong authentication.
Error: Can't open display: localhost:10.0

@joshenders , thanks for this!

@andrey-malets glad it was helpful!