By default the referral link sent with Points and Rewards extension redirects to the home page of the store.
If you want referrals navigated to the customer login page instead of the home page of the store, the following code modifications will be required:
Navigate to app\code\local\AW\Points\Helper\Data.php. Make a back up of Data.php by copying and renaming it to Data.php.backup in case original file will be required in future.
Open Data.php and find the line:
const PAGE_TO_REDIRECT = "/"; // redirect to homepage
And either comment it out by typing in // before it or delete the whole line.
Then uncomment (by deleting // before the line) the line:
//const PAGE_TO_REDIRECT = "customer/account/login/"; //redirect to loginpage
Now Points and Rewards extension's referral link will redirect referrals to the customer login page of your store.