How Would I Accomplish Single Sign On Between Two Wordpress sites?

Hey guys! Hopefully someone can send me in the right direction. How would I go by creating a single sign on feature between two of my wordpress websites? Is it possible? If so, how do you recommend doing this? I was also looking some into the (Auth Zero) website, do you think their services could make this a possibility? Really, if someone logs into the .com I want them to also be logged into the .net.

Thanks for any guidance and direction!