KaeruCT

This plugin allows passwords for password-protected pages/posts to be passed directly through the URL.
The query string parameter that should contain the password is <code>pw</code>.
For example, if the URL of your post is <code>http://myblog.com/password-protected-page/</code> and the password is <code>PASSWORD</code>, 
then just append <code>?pw=PASSWORD</code> to it.
If the URL already contains a query string (for example, <code>http://myblog.com/?p=5</code>), then be sure to append <code>&pw=PASSWORD</code> instead.

Password Passthrough

This plugin allows passwords for password-protected pages/posts to be passed directly through the URL.

brechtryckaert

Limiting the cookie expire time of password protected posts. By default the cookie set when entering a password to access a password-protected post will be active for 10 days. This plugin turns this cookie into a session-based cookie. This means your visitor will need to re-enter the password if the browser was closed prior to revisiting the post.

Instant Cookie Expire

This plugin turns the cookie for a password-protected post into a session-based cookie.

Password Passthrough vs Instant Cookie Expire