Implement ldap group search functionality

Gemfile

@@ -30,6 +30,7 @@ gem 'gitlab-grack', '~> 1.0.1', require: 'grack'
 
 # LDAP Auth
 gem 'gitlab_omniauth-ldap', '1.0.3', require: "omniauth-ldap"
+gem 'net-ldap'
 
 # Syntax highlighter
 gem "gitlab-pygments.rb", '~> 0.3.2', require: 'pygments.rb'

Gemfile.lock

@@ -591,6 +591,7 @@ DEPENDENCIES
   minitest (~> 4.7.0)
   modernizr (= 2.6.2)
   mysql2
+  net-ldap
   omniauth (~> 1.1.3)
   omniauth-github
   omniauth-google-oauth2

lib/gitlab/ldap.rb

+module Gitlab
+  class LDAP
+    attr_reader :ldap
+
+    def initialize
+      @ldap = Net::LDAP.new(
+        host: config['host'],
+        port: config['port'],
+        auth: {
+          method: config['method'],
+          username: config['bind_dn'],
+          password: config['password']
+        }
+      )
+    end
+
+    # Get LDAP groups from ou=Groups
+    #
+    # cn - filter groups by name
+    #
+    # Ex.
+    #   groups("dev*") # return all groups start with 'dev'
+    #
+    def groups(cn = "*")
+      options = {
+        base: "ou=Groups,#{config['base']}",
+        filter: Net::LDAP::Filter.eq("cn", cn)
+      }
+
+      ldap.search(options)
+    end
+
+    private
+
+    def config
+      @config ||= Gitlab.config.ldap
+    end
+  end
+end