The OpenID Login plugin provides support to allow users to log in via OpenID, a popular single-sign-on protocol used by Google, Yahoo, and many other large sites. Users will then have the option of re-using an existing account to log in rather than being required to create a new one specifically for your site. When someone logs in via OpenID, a CWIS account is automatically created for them, and their user information (e.g., name, email) is obtained from their OpenId provider. The plugin only provides the ability to allow users to log in with OpenID credentials from others sites; to allow users to log into other sites using OpenID credentials from your site, install the OpenID Server plugin.
Some OpenId providers may only allow OpenId authentication over a secure connection. To use those providers, you'll need the PHP OpenSSL module enabled on your server. The PHP Configuration Summary accessible via the CWIS Administration page will indicate if OpenSSL is available.