Bypass signup domain validation for external users

Fixes #25279

app/models/user.rb

@@ -119,7 +119,7 @@ class User < ActiveRecord::Base
   validates :avatar, file_size: { maximum: 200.kilobytes.to_i }
 
   before_validation :generate_password, on: :create
-  before_validation :signup_domain_valid?, on: :create
+  before_validation :signup_domain_valid?, on: :create, if: ->(user) { !user.created_by_id }
   before_validation :sanitize_attrs
   before_validation :set_notification_email, if: ->(user) { user.email_changed? }
   before_validation :set_public_email, if: ->(user) { user.public_email_changed? }

changelogs/unreleased/bypass-email-domain-validation-when-created-by-admin.yml

+---
+title: Bypass email domain validation when a user is created by an admin.
+merge_request: 8575
+author: Reza Mohammadi @remohammadi

doc/user/admin_area/settings/sign_up_restrictions.md

 # Sign-up restrictions
 
+You can block email addresses of specific domains, or whitelist only some
+specifc domains via the **Application Settings** in the Admin area.
+
+>**Note**: These restrictions are only applied during sign-up. An admin is
+able to add add a user through the admin panel with a disallowed domain. Also
+note that the users can change their email addresses after signup to
+disallowed domains.
+
+## Whitelist email domains
+
+> [Introduced][ce-598] in GitLab 7.11.0
+
+You can restrict users to only signup using email addresses matching the given
+domains list.
+
 ## Blacklist email domains
 
 > [Introduced][ce-5259] in GitLab 8.10.
@@ -9,13 +24,16 @@ from creating an account on your GitLab server. This is particularly useful to
 prevent spam. Disposable email addresses are usually used by malicious users to
 create dummy accounts and spam issues.
 
+## Settings
+
 This feature can be activated via the **Application Settings** in the Admin area,
 and you have the option of entering the list manually, or uploading a file with
 the list.
 
-The blacklist accepts wildcards, so you can use `*.test.com` to block every
-`test.com` subdomain, or `*.io` to block all domains ending in `.io`. Domains
-should be separated by a whitespace, semicolon, comma, or a new line.
+Both whitelist and blacklist accept wildcards, so for example, you can use
+`*.company.com` to accept every `company.com` subdomain, or `*.io` to block all
+domains ending in `.io`. Domains should be separated by a whitespace,
+semicolon, comma, or a new line.
 
 ![Domain Blacklist](img/domain_blacklist.png)
 

spec/models/user_spec.rb

@@ -141,6 +141,11 @@ describe User, models: true do
           user = build(:user, email: "example@test.com")
           expect(user).to be_invalid
         end
+
+        it 'accepts example@test.com when added by another user' do
+          user = build(:user, email: "example@test.com", created_by_id: 1)
+          expect(user).to be_valid
+        end
       end
 
       context 'domain blacklist' do
@@ -159,6 +164,11 @@ describe User, models: true do
             user = build(:user, email: 'info@example.com')
             expect(user).not_to be_valid
           end
+
+          it 'accepts info@example.com when added by another user' do
+            user = build(:user, email: 'info@example.com', created_by_id: 1)
+            expect(user).to be_valid
+          end
         end
 
         context 'when a signup domain is blacklisted but a wildcard subdomain is allowed' do