Set auth method for Global Catalog explicitly to :simple

lib/github/ldap.rb

@@ -217,7 +217,7 @@ module GitHub
       if active_directory_capability?
         @global_catalog_connection ||= Net::LDAP.new({
           host: @connection.host,
-          auth: {username: admin_user, password: admin_password},
+          auth: {method: :simple, username: admin_user, password: admin_password},
           instrumentation_service: instrumentation_service,
           port: 3268,
         })

test/ldap_test.rb

@@ -153,6 +153,8 @@ module GitHubLdapTestCases
     global_catalog = @ldap.global_catalog_connection
     instrumentation_service = global_catalog.instance_variable_get(:@instrumentation_service)
 
+    auth = global_catalog.instance_variable_get(:@auth)
+    assert_equal :simple, auth[:method]
     assert_equal "localhost", global_catalog.host
     assert_equal 3268, global_catalog.port
     assert_equal "MockInstrumentationService", instrumentation_service.class.name