Using inbuilt functions of Wordpress user can do auto login for the application. As a client requirement my wordpress need auto login using user email id, so after doing some google i came to know about function wp_set_current_user() which sets the current user (but does not do auto login) and wp_set_auth_cookie sets the authentication cookies using User ID.
Below is the complete code i got it from the function page:
My current Wordpress version: 3.9