Open/close LDAP in ApplicationController

By opening the LDAP connection at the controller level we can reuse it
for all LDAP queries during the request.

CHANGELOG

@@ -17,6 +17,7 @@ v 6.7.0
   - Add GFM autocompletion for MergeRequests (Robert Speicher)
   - Add webhook when a new tag is pushed (Jeroen van Baarsen)
   - Add button for toggling inline comments in diff view
+  - Reuse the GitLab LDAP connection within each request
 v 6.6.2
   - Fix 500 error on branch/tag create or remove via UI

app/controllers/application_controller.rb

@@ -182,13 +182,15 @@ class ApplicationController < ActionController::Base
   def ldap_security_check
     if current_user && current_user.requires_ldap_check?
-      if gitlab_ldap_access.allowed?(current_user)
-        current_user.last_credential_check_at = Time.now
-        current_user.save
-      else
-        sign_out current_user
-        flash[:alert] = "Access denied for your LDAP account."
-        redirect_to new_user_session_path
+      gitlab_ldap_access do |access|
+        if access.allowed?(current_user)
+          current_user.last_credential_check_at = Time.now
+          current_user.save
+        else
+          sign_out current_user
+          flash[:alert] = "Access denied for your LDAP account."
+          redirect_to new_user_session_path
+        end
       end
     end
   end
@@ -198,8 +200,8 @@ class ApplicationController < ActionController::Base
     @event_filter ||= EventFilter.new(filters)
   end
-  def gitlab_ldap_access
-    Gitlab::LDAP::Access.new
+  def gitlab_ldap_access(&block)
+    Gitlab::LDAP::Access.open { |access| block.call(access) }
   end
   # JSON for infinite scroll via Pager object