rails 单点认证资源

https://github.com/fortuity/rails3-subdomain-devise/wiki/Tutorial-(Walkthrough)

http://excid3.com/blog/sharing-a-devise-user-session-across-subdomains-with-rails-3/

http://stackoverflow.com/questions/16475910/rails-devise-login-from-a-different-domain

http://blog.joshsoftware.com/2010/12/16/multiple-applications-with-devise-omniauth-and-single-sign-on/

https://github.com/joshsoftware/sso-devise-omniauth-provider