Authentication
From WebOS
OpenID and HTTP Authentication are authentication standards.
[edit] OpenAuth
Specifically LOGIN and LOGOUT.
To login, redirect to:
http(s)://api.screenname.aol.com/auth/login?devId=${like an API key}&f=${format of response data}&succUrl=${URL to return to}&s=${optional username}&language=${language}&tokenType=${how long should session last?}&c=${callback (for jsonp)}&r=${id}
(succUrl defaults to referrer header.)
After user logs in at AOL they will redirect to succUrl?response_data (or to ?res=encoded_response_data). token_a (or a) is the session id, pass it with API calls.
LOGOUT is similar, but kills all current session tokens for user.
[edit] Other
Others seem similar. Facebook and Flickr especially. Google and Yahoo, etc, slightly more complicated (custom HTTP headers).

