When switching to root after the typical SSH with X11 forwarding enabled this error can appear:
$ X11 connection rejected because of wrong authentication. $ Error: Can't open display: localhost:10.0
The workaround seems to include copying the MIT-MAGIC-COOKIE-1 from the user who ssh'd in to the root user using xauth. Here's how:
First verify the $DISPLAY being used and list the MIT-MAGIC-COOKIE-1 used for it :
$ echo $DISPLAY localhost:10.0 $ xauth list srv001/unix:10 MIT-MAGIC-COOKIE-1 b7ff39ed41f66cfe8fe439ed99e582ba
Next switch to root and copy the whole line that was listed and then add it to the root profile:
# xauth add srv001/unix:10 MIT-MAGIC-COOKIE-1 b7ff39ed41f66cfe8fe439ed99e582ba
Now assuming everything is correct in the standard ssh_config the error should go away and a window will before forwarded through the pipe.