users: require email verification for signups from proxies.

Require users who signup using proxies to verify their email addresses
before they can perform any edits. For verification purposes, the email
must be a nondisposable address from a whitelist of trusted email
providers.

test/functional/emails_controller_test.rb

@@ -85,6 +85,30 @@ class EmailsControllerTest < ActionDispatch::IntegrationTest
           assert_equal(false, @user.reload.email_address.is_verified)
         end
       end
+
+      context "with a nondisposable email address" do
+        should "mark the user as verified" do
+          Danbooru.config.stubs(:email_domain_verification_list).returns(["gmail.com"])
+          @user.email_address.update!(address: "test@gmail.com")
+          get email_verification_url(@user)
+
+          assert_redirected_to @user
+          assert_equal(true, @user.reload.email_address.is_verified)
+          assert_equal(true, @user.is_verified)
+        end
+      end
+
+      context "with a disposable email address" do
+        should "not mark the user as verified" do
+          Danbooru.config.stubs(:email_domain_verification_list).returns([])
+          @user.email_address.update!(address: "test@mailinator.com")
+          get email_verification_url(@user)
+
+          assert_redirected_to @user
+          assert_equal(true, @user.reload.email_address.is_verified)
+          assert_equal(false, @user.is_verified)
+        end
+      end
     end
   end
 end