On Application Settings Page let the user select the enabled OAuth Sign in...

On Application Settings Page let the user select the enabled OAuth Sign in sources instead of the disabled ones

app/controllers/admin/application_settings_controller.rb

@@ -53,14 +53,13 @@ class Admin::ApplicationSettingsController < Admin::ApplicationController
       end
     end
 
-    disabled_oauth_sign_in_sources = params[:application_setting][:disabled_oauth_sign_in_sources]
-    if disabled_oauth_sign_in_sources.nil?
-      params[:application_setting][:disabled_oauth_sign_in_sources] = []
-    else
-      disabled_oauth_sign_in_sources.map! do |source|
-        source.to_str
-      end
-    end
+    enabled_oauth_sign_in_sources = params[:application_setting][:enabled_oauth_sign_in_sources]
+
+    params[:application_setting][:disabled_oauth_sign_in_sources] =
+      AuthHelper.button_based_providers.map(&:to_s) -
+      (enabled_oauth_sign_in_sources.nil? ? [] : enabled_oauth_sign_in_sources)
+
+    params[:application_setting].delete(:enabled_oauth_sign_in_sources)
 
     params.require(:application_setting).permit(
       :default_projects_limit,
@@ -105,6 +104,7 @@ class Admin::ApplicationSettingsController < Admin::ApplicationController
       :metrics_packet_size,
       restricted_visibility_levels: [],
       import_sources: [],
+      enabled_oauth_sign_in_sources: [],
       disabled_oauth_sign_in_sources: []
     )
   end

app/helpers/application_settings_helper.rb

@@ -63,13 +63,13 @@ module ApplicationSettingsHelper
 
   def oauth_providers_checkboxes(help_block_id)
     button_based_providers.map do |source|
-      checked = current_application_settings.disabled_oauth_sign_in_sources.include?(source.to_s)
+      disabled = current_application_settings.disabled_oauth_sign_in_sources.include?(source.to_s)
       css_class = 'btn'
-      css_class += ' active' if checked
-      checkbox_name = 'application_setting[disabled_oauth_sign_in_sources][]'
+      css_class += ' active' unless disabled
+      checkbox_name = 'application_setting[enabled_oauth_sign_in_sources][]'
 
       label_tag(checkbox_name, class: css_class) do
-        check_box_tag(checkbox_name, source, checked,
+        check_box_tag(checkbox_name, source, !disabled,
                       autocomplete: 'off',
                       'aria-describedby' => help_block_id) + Gitlab::OAuth::Provider.label_for(source)
       end

app/views/admin/application_settings/_form.html.haml

@@ -111,7 +111,7 @@
             Sign-in enabled
     - if omniauth_enabled? && !button_based_providers.empty?
       .form-group
-        = f.label :disable_oauth_signin_sources, 'Disable OAuth Sign-In sources', class: 'control-label col-sm-2'
+        = f.label :enabled_oauth_sign_in_sources, 'Enabled OAuth Sign-In sources', class: 'control-label col-sm-2'
         .col-sm-10
           - data_attrs = { toggle: 'buttons' }
           .btn-group{ data: data_attrs }