Incompatible with SSL login/admin

It is an insecure practice to be offering any login or admin interface without SSL, which is why WP has force_ssl_login and force_ssl_admin config variables. Unfortunately, this plugin assumes that all URL’s start with ‘http://’ and creates an infinite loop of redirects if you are configured to protect your login and admin mechanisms from casual sniffers.

http://wordpress.org/extend/plugins/basic-authentication/