How do users can login automatically through URL when they click on the link received in Email In Drupal 7, I am sending E-mail to each user with some content. Here I need to send link to automatically login through URL means when they click on the link they should redirect to the site and submit the form. This form should submitted by only authenticated users. How to generate those Unique URLs. Is there any module for this or give me any ideas please.
Try the Login one time module


  Login one time provides the ability to email one-time login links to users. You can also choose the pages they will land on.


Another module is urllogin


  This module provides a way to transparently log users into the web site when they follow a link. The primary use is for mass email where users are send individualized URL’s which take them to a page on the site, in a “logged in” state. Every effort has been made to minimize the potential security risks.