Populate custom fields automatically

It makes perfect sense that fields from `Additional attributes`
are populated automatically, instead of user having to hardcode
how the fields are populated in source code of this module.

This implementation has no support for translations or more
complex fields. But it should work fine with basic fields that
have simple value column.

The implementation is inspired by comment by @pablo-tapia in
AngelAlvarado#4.

includes/simplesamlphp_auth.drupal.inc

@@ -137,7 +137,12 @@ class SimpleSAML_Drupal {
                     if ($key == 'cs_fields') {
                         foreach ($data as $additional_data) {
                             $additional_data = explode(':', $additional_data);
-                            $this->_simplesaml_auth_source->{$additional_data[0]} = $additional_data[1];
+                            if (isset($additional_data[1]) && !empty($additional_data[1])) {
+								// Wrap all custom fields around the custom fields property to access them later
+								$this->_simplesaml_auth_source->custom_fields[$additional_data[0]] = $additional_data[1];
+							} else {
+								watchdog('simplesamlphp_auth', 'Unable to load custom field into the SAML object, verify that you\'re using the correct operator', array(), WATCHDOG_DEBUG);
+							} // end if - else
                         } // end foreach
                     } // end if
                     $this->_simplesaml_auth_source->{$key} = $data;

simplesamlphp_auth.inc

@@ -133,22 +133,26 @@ function _simplesaml_auth_user_register($authname) {
                 'timezone' => date_default_timezone_get(),
             );
 
+			/**
+			 * Populate custom fields
+			 */
+			if (isset($simplesamlphp_authsource->custom_fields)) {
+				foreach($simplesamlphp_authsource->custom_fields as $field_name => $attribute_name) {
+					if (!empty($field_name) && !empty($attribute_name)) {
+						$userinfo[$field_name] = array(
+							'und' => array(array('value' => $simplesamlphp_drupal->getAttrsFromAssertion($attribute_name)))
+						);
+					} // end if
+				} // end foreach
+			} // end if
+
             /**
-             * If you want, you can place more custom fields and populate them here
-             * @example
-             * if (isset($simplesamlphp_authsource->firstname)) {
-             *   $userinfo['field_first_name'] = array(
-             *     'und' => array(array('value' => $simplesamlphp_drupal->getAttrsFromAssertion($simplesamlphp_authsource->firstname)))
-             *   );
-             * }
-             */
-            /**
-             * Populate roles 
+             * Populate roles
              */
             $roles = array();
             try {
                 // Get SAML attributes
-                $attrs = $simplesamlphp_auth_as->getAttributes();                
+                $attrs = $simplesamlphp_auth_as->getAttributes();
 
                 if ($simplesamlphp_authsource->syncroles) {
                     // The roles provided by the IdP.