Finish email allow/deny list naming migration (#30530)

app/validators/user_email_validator.rb

@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+class UserEmailValidator < ActiveModel::Validator
+  def validate(user)
+    return if user.valid_invitation? || user.email.blank?
+
+    user.errors.add(:email, :blocked) if blocked_email_provider?(user.email, user.sign_up_ip)
+    user.errors.add(:email, :taken) if blocked_canonical_email?(user.email)
+  end
+
+  private
+
+  def blocked_email_provider?(email, ip)
+    disallowed_through_email_domain_block?(email, ip) || disallowed_through_configuration?(email) || not_allowed_through_configuration?(email)
+  end
+
+  def blocked_canonical_email?(email)
+    CanonicalEmailBlock.block?(email)
+  end
+
+  def disallowed_through_email_domain_block?(email, ip)
+    EmailDomainBlock.block?(email, attempt_ip: ip)
+  end
+
+  def not_allowed_through_configuration?(email)
+    return false if Rails.configuration.x.email_domains_allowlist.blank?
+
+    domains = Rails.configuration.x.email_domains_allowlist.gsub('.', '\.')
+    regexp  = Regexp.new("@(.+\\.)?(#{domains})$", true)
+
+    email !~ regexp
+  end
+
+  def disallowed_through_configuration?(email)
+    return false if Rails.configuration.x.email_domains_denylist.blank?
+
+    domains = Rails.configuration.x.email_domains_denylist.gsub('.', '\.')
+    regexp  = Regexp.new("@(.+\\.)?(#{domains})", true)
+
+    regexp.match?(email)
+  end
+end