remote login using ajax

I have a multisite install on my server with many related blogs, each of which is visible only to users that have been added as subscribers to that blog (an option of the More Privacy Options).

I need to enable users to logon to one of these blogs, but from another website. So on http://www.someotherdomain.com, there will be data fields (username, password, URL) and a login button. When entered correctly, a new window must open and display the blog (specified by the URL). In other words, the authentication must happen on a different website.

I found this post which aludes to an ajax solution.
http://ww.wp.xz.cn/support/topic/remote-login-using-curl?replies=4
Can anyone please advise me on whether this is the most appropriate solution?

Another option that come to mind are using an iframe to display a portion of my website so that it appears on the remote site, but when login occurs, it is actually between my site and the client browser so cookies.

Other suggestions are welcome. I assume I’m not the first person who has needed this.