cuve

With this plugin, you can ask users to authenticate before they can see your WordPress site. 
You can either use the WordPress logins to authenticate, or a given password. 
This plugin can be useful when your website is still under construction or in beta fase. 
No HTTP Authentication is used.

Basic Authentication

With this plugin, you can ask users to authenticate before they can see your Wordpress site.

Matthias Pfefferle

Will Norris

OpenID is an <a href="http://openid.net/" rel="nofollow ugc">open standard</a> that allows users to authenticate to websites without having to create a new password. This plugin allows users to login to their local WordPress account using an OpenID, as well as enabling commenters to leave authenticated comments with OpenID. The plugin also includes an OpenID provider, enabling users to login to OpenID-enabled sites using their own personal WordPress account. <a href="https://wordpress.org/plugins/xrds-simple/" rel="ugc">XRDS-Simple</a> is required for the OpenID Provider and some features of the OpenID Consumer.
Developer documentation, which includes all of the public methods and hooks for integrating with and extending the plugin, can be found <a href="http://wiki.diso-project.org/wordpress-openid-api" rel="nofollow ugc">here</a>.

OpenID

Allows WordPress to provide and consumer OpenIDs for authentication of users and comments.

Basic Authentication vs OpenID