Single Sign On/integration

I have a food recipe website with very limited user profile features. I would love to be able to use Elgg as the profile for our users instead of the existing one. Today our users need to be signed in to be able to: submit recipe, leave comments, rate recipe etc. I am therefore looking at the option of Single Sign On. It would also be great if the users could have a documentation/links on their profiles to all the recipes they have posted. How can I make this happen? Any ideas?