Add option to use the servers uuid cache/lookup facility (#354)

bukkit/src/main/java/me/lucko/luckperms/bukkit/LPBukkitPlugin.java

@@ -510,6 +510,17 @@ public class LPBukkitPlugin extends JavaPlugin implements LuckPermsPlugin {
         return getServer().getPlayer(uuidCache.getExternalUUID(user.getUuid()));
     }
 
+    @Override
+    public Optional<UUID> lookupUuid(String username) {
+        try {
+            //noinspection deprecation
+            return Optional.ofNullable(getServer().getOfflinePlayer(username)).flatMap(p -> Optional.ofNullable(p.getUniqueId()));
+        } catch (Exception e) {
+            e.printStackTrace();
+            return Optional.empty();
+        }
+    }
+
     @Override
     public Contexts getContextForUser(User user) {
         Player player = getPlayer(user);

bukkit/src/main/resources/config.yml

@@ -66,6 +66,10 @@ apply-global-world-groups: true
 # forwarding.
 use-server-uuids: true
 
+# If the servers own UUID cache/lookup facility should be used when there is no record for a player
+# in the LuckPerms cache.
+use-server-uuid-cache: false
+
 # If the plugin should send log notifications to users whenever permissions are modified.
 log-notify: true