Unique email domain allowed

This PR add a restriction in case the user registration is needed, only
from a single mail domain.

##How to test
1. Go to the configs in the user manager
2. Fill the field "Unique mail domain", and save
3. Go to the frontend, and try to register with a different domain than
the field "Unique mail domain". A error message will show up, saying,
"Your mail domain xxx is not allowed".

administrator/components/com_users/config.xml

@@ -33,6 +33,13 @@
 			checksuperusergroup="1"
 		/>
 
+		<field
+ 			name="allowedMailDomain"
+ 			type="text"
+			label="COM_USERS_CONFIG_FIELD_ALLOWED_MAILDOMAIN_LABEL"
+			description="COM_USERS_CONFIG_FIELD_ALLOWED_MAILDOMAIN_DESC"
+		/>
+
 		<field
 			name="sendpassword"
 			type="radio"

administrator/language/en-GB/en-GB.com_users.ini

@@ -15,6 +15,8 @@ COM_USERS_BATCH_OPTIONS="Batch process the selected users"
 COM_USERS_BATCH_SET="Set To Group"
 COM_USERS_CATEGORIES_TITLE="User Notes: Categories"
 COM_USERS_CATEGORY_HEADING="Category"
+COM_USERS_CONFIG_FIELD_ALLOWED_MAILDOMAIN_DESC="Mail domain only allowed to register on the site. Example: gmail.com"
+COM_USERS_CONFIG_FIELD_ALLOWED_MAILDOMAIN_LABEL="Unique mail domain"
 COM_USERS_CONFIG_FIELD_ALLOWREGISTRATION_DESC="If set to Yes, new Users are allowed to self-register."
 COM_USERS_CONFIG_FIELD_ALLOWREGISTRATION_LABEL="Allow User Registration"
 COM_USERS_CONFIG_FIELD_CAPTCHA_DESC="Select the captcha plugin that will be used in the registration, password and username reminder forms. You may need to enter required information for your captcha plugin in the Plugin Manager.<br />If 'Use Global' is selected, make sure a captcha plugin is selected in Global Configuration."

components/com_users/controllers/registration.php

@@ -105,7 +105,7 @@ public function activate()
 	 *
 	 * @since   1.6
 	 */
-	public function register()
+	public function register() 
 	{
 		// Check for request forgeries.
 		$this->checkToken();

components/com_users/models/registration.php

@@ -422,6 +422,16 @@ public function register($temp)
 		$data['password'] = $data['password1'];
 		$useractivation = $params->get('useractivation');
 		$sendpassword = $params->get('sendpassword', 1);
+		$allowedMailDomain = $params->get('allowedMailDomain');
+
+		// Check in case can only register under a single mail domain
+		$userMailDomain = explode('@',$data['email']);
+		if (!empty($allowedMailDomain) && $userMailDomain[1] != $allowedMailDomain) 
+		{
+			$this->setError(JText::sprintf('COM_USERS_REGISTRATION_USER_MAIL_DOMAIN_NOT_ALLOWED_MESSAGE', $userMailDomain[1]));
+
+			return false;
+		}
 
 		// Check if the user needs to activate their account.
 		if (($useractivation == 1) || ($useractivation == 2))

language/en-GB/en-GB.com_users.ini

@@ -126,6 +126,7 @@ COM_USERS_REGISTRATION_SAVE_FAILED="Registration failed: %s"
 COM_USERS_REGISTRATION_SAVE_SUCCESS="Thank you for registering. You may now log in using the username and password you registered with."
 COM_USERS_REGISTRATION_SEND_MAIL_FAILED="An error was encountered while sending the registration email. A message has been sent to the administrator of this site."
 COM_USERS_REGISTRATION_VERIFY_SUCCESS="Your email address has been verified. Once an administrator approves your account you will be notified by email and you can login to the site."
+COM_USERS_REGISTRATION_USER_MAIL_DOMAIN_NOT_ALLOWED_MESSAGE="Your mail domain <strong>%s</strong> is not allowed"
 COM_USERS_REMIND="Reminder"
 COM_USERS_REMIND_DEFAULT_LABEL="Please enter the email address associated with your User account. Your username will be emailed to the email address on file."
 COM_USERS_REMIND_EMAIL_LABEL="Your Email"