Kevin Muldoon reviews some options for integrating single sign-on using social media sites into your WordPress blog and I went with “WP Social Login.”
It is very easy to set up and to create the integration keys with the sites. The data is stored on your site and you have control over how it is used. You can reassure your clients that their contact information is safe.
Read the review in Smashing Magazine, May 19, 2012 called How To Log In To WordPress Using A Social Network.