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 pw.
For example, if the URL of your post is http://myblog.com/password-protected-page/ and the password is PASSWORD,
then just append ?pw=PASSWORD to it.
If the URL already contains a query string (for example, http://myblog.com/?p=5), then be sure to append &pw=PASSWORD instead.