Question: I'm trying to determine if there is a Yahoo API that I can use to create authentication based on membership in a Yahoo Group for a non-Yahoo website writte in ASP.NET. Basically, if a person is a member of a particular group, then they would be able to Login to this website.

Our club has an existing Yahoo site, but we'd like to disconnect from Yahoo while retaining the emailing capability that it offers, and I'd like to keep the number of places to be members of to a minimum. So if a person signs up for the Yahoo group, I'd like them automatically be able to login to the non-Yahoo site without any other steps.

Answer: 
You can check this PHP code for an example: <http://drupal.org/project/yahoo_bbauth>

And this example:

<http://upcoming.yahoo.com/services/api/group.getMyGroups.php>
[open source - does a Yahoogroups api exist? - Stack Overflow](https://stackoverflow.com/questions/1624147/does-a-yahoogroups-api-exist)

Based on this post from Oct 2009 there is no Yahoo! Groups API yet and if there will be one it'll be listed on the YUI developer page 

This index page of YDN Documentation [Yahoo! Developer Network - Developer Documentation](http://developer.yahoo.com/documentation) indicates there is no Yahoo! Groups API at this time still.