I have been asked to implement a cross site login solution in Zend Framework.
I have thought about perhaps using OpenID, are there any other solutions to make a login persist across many sites?
In some ways a closed system hosted by us would suit better.
I would go with openid (see http://framework.zend.com/manual/en/zend.openid.provider.html) but you can also make the login action connect to common database...
I think you can't easily make user connected across different domains as long as the cookies are domain specific...