Set XAUTHLOCALHOSTNAME to the hostname for local logins to avoid issues in the
session in case the hostname changes.

Index: lightdm-1.30.0/src/seat-local.c
===================================================================
--- lightdm-1.30.0.orig/src/seat-local.c
+++ lightdm-1.30.0/src/seat-local.c
@@ -289,6 +289,7 @@ seat_local_run_script (Seat *seat, Displ
         const gchar *path = x_server_local_get_authority_file_path (X_SERVER_LOCAL (display_server));
         process_set_env (script, "DISPLAY", x_server_get_address (X_SERVER (display_server)));
         process_set_env (script, "XAUTHORITY", path);
+        process_set_env (script, "XAUTHLOCALHOSTNAME", g_get_host_name ());
     }
 
     SEAT_CLASS (seat_local_parent_class)->run_script (seat, display_server, script);
Index: lightdm-1.30.0/src/x-authority.c
===================================================================
--- lightdm-1.30.0.orig/src/x-authority.c
+++ lightdm-1.30.0/src/x-authority.c
@@ -68,8 +68,8 @@ x_authority_new_cookie (guint16 family,
 XAuthority *
 x_authority_new_local_cookie (const gchar *number)
 {
-    gchar hostname[1024];
-    gethostname (hostname, 1024);
+    const gchar *hostname;
+    hostname = g_get_host_name ();
     return x_authority_new_cookie (XAUTH_FAMILY_LOCAL, (guint8 *) hostname, strlen (hostname), number);
 }
 
Index: lightdm-1.30.0/src/x-server.c
===================================================================
--- lightdm-1.30.0.orig/src/x-server.c
+++ lightdm-1.30.0/src/x-server.c
@@ -15,6 +15,7 @@
 
 #include "x-server.h"
 #include "configuration.h"
+#include "x-server-local.h"
 
 typedef struct
 {
@@ -161,6 +162,8 @@ x_server_connect_session (DisplayServer
     else
         l_debug (session, "Not setting XDG_VTNR");
 
+    if (IS_X_SERVER_LOCAL (display_server))
+        session_set_env (session, "XAUTHLOCALHOSTNAME", g_get_host_name ());
     session_set_env (session, "DISPLAY", x_server_get_address (X_SERVER (display_server)));
     session_set_xdisplay (session, x_server_get_address (X_SERVER (display_server)));
     session_set_remote_host_name (session, x_server_get_hostname (X_SERVER (display_server)));