Add new table to store email domain

In order to save user preferences regarding
user emails allowed to be invited to group

Add foreign_key and down method

Change adding foreign key

Add partial call to view

Add changelog entry

Fix schema

app/views/groups/settings/_permissions.html.haml

@@ -18,6 +18,7 @@
           %span.descr.text-muted= share_with_group_lock_help_text(@group)
     = render_if_exists 'groups/settings/ip_restriction', f: f, group: @group
+    = render_if_exists 'groups/settings/allowed_email_domain', f: f, group: @group
     = render 'groups/settings/lfs', f: f
     = render 'groups/settings/project_creation_level', f: f, group: @group
     = render 'groups/settings/subgroup_creation_level', f: f, group: @group

changelogs/unreleased/10972-be-allow-restricting-group-members-by-a-domain-whitelist-ce.yml

+---
+title: Add new table to store email domain per group
+merge_request: 31071
+author:
+type: added

db/migrate/20190723153247_create_allowed_email_domains_for_groups.rb

+# frozen_string_literal: true
+
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class CreateAllowedEmailDomainsForGroups < ActiveRecord::Migration[5.2]
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  def change
+    create_table :allowed_email_domains do |t|
+      t.timestamps_with_timezone null: false
+      t.references :group, references: :namespace,
+        column: :group_id,
+        type: :integer,
+        null: false,
+        index: true
+      t.foreign_key :namespaces, column: :group_id, on_delete: :cascade
+      t.string :domain, null: false, limit: 255
+    end
+  end
+end

db/schema.rb

@@ -26,6 +26,14 @@ ActiveRecord::Schema.define(version: 2019_08_15_093949) do
     t.integer "cached_markdown_version"
   end
+  create_table "allowed_email_domains", force: :cascade do |t|
+    t.datetime_with_timezone "created_at", null: false
+    t.datetime_with_timezone "updated_at", null: false
+    t.integer "group_id", null: false
+    t.string "domain", limit: 255, null: false
+    t.index ["group_id"], name: "index_allowed_email_domains_on_group_id"
+  end
+
   create_table "analytics_cycle_analytics_group_stages", force: :cascade do |t|
     t.datetime_with_timezone "created_at", null: false
     t.datetime_with_timezone "updated_at", null: false
@@ -3670,6 +3678,7 @@ ActiveRecord::Schema.define(version: 2019_08_15_093949) do
     t.index ["type"], name: "index_web_hooks_on_type"
   end
+  add_foreign_key "allowed_email_domains", "namespaces", column: "group_id", on_delete: :cascade
   add_foreign_key "analytics_cycle_analytics_group_stages", "labels", column: "end_event_label_id", on_delete: :cascade
   add_foreign_key "analytics_cycle_analytics_group_stages", "labels", column: "start_event_label_id", on_delete: :cascade
   add_foreign_key "analytics_cycle_analytics_group_stages", "namespaces", column: "group_id", on_delete: :cascade

doc/user/group/index.md

@@ -350,6 +350,38 @@ Restriction currently applies to UI, API access is not restricted.
 To avoid accidental lock-out, admins and group owners are are able to access
 the group regardless of the IP restriction.
+#### Allowed domain restriction **(PREMIUM ONLY)**
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab-ee/issues/7297) in
+[GitLab Premium](https://about.gitlab.com/pricing/) 12.2.
+
+You can restrict access to groups and their underlying projects by
+allowing only users with email addresses in particular domains to be added to the group.
+
+Add email domains you want to whitelist and users with emails from different 
+domains won't be allowed to be added to this group.
+
+Some domains cannot be restricted. These are the most popular public email domains, such as:
+
+- `gmail.com`
+- `yahoo.com`
+- `hotmail.com`
+- `aol.com`
+- `msn.com`
+- `hotmail.co.uk`
+- `hotmail.fr`
+- `live.com`
+- `outlook.com`
+- `icloud.com`
+
+To enable this feature:
+
+1. Navigate to the group's **Settings > General** page.
+1. Expand the **Permissions, LFS, 2FA** section, and enter domain name into **Restrict membership by email** field.
+1. Click **Save changes**.
+
+This will enable the domain-checking for all new users added to the group from this moment on.
+
 #### Group file templates **(PREMIUM)**
 Group file templates allow you to share a set of templates for common file