src/include/http-auth.properties.in

#
# The HTTP header containing the username of the authenticated user.
#
# This property is optional. If not specified, `REMOTE_USER` will be used by
# default. If your authentication system uses a different HTTP header you can
# use this option to override it and specify the header for Guacamole to
# expect.
#
http-auth-header: REMOTE_USER