There are many technologies available to implement a system of registration/un-registration of users for an online service.
Let's imagine a software engineer having knowledge in HTML + CSS + Java. What would be the most efficient way to implement these registration pages (login + email, click on link in email to confirm registration + click on web page link to un-register). A database is already set-up.
Is there an out-of-the-bow framework/solution he could use/configure? If yes which?
Should he invest time in learning a technology that will help him achieve this? If yes which? If so, it should be a battle tested technology, well documented and with forums where support can easily be found.
Are there template projects or codes examples he could use or refer to to implement these pages?
The solution should be open source/free.