title: How to accomplish multiple authentication using Devise Omniauth + (Facebook , Twitter, Google )?
body: <p>I have implemented the Devise Omniauth authentication in my Rails application successfully using the following tutorial by git
  <a href="https://github.com/plataformatec/devise/wiki/OmniAuth%3a-Overview">OmniAuth: Overview</a></p>
  
  <p>But it will not support multiple authentications , may be you all know that , and have faced the same issue before, but if you people have tweaked the same problem successfully please let me know the solution .</p>
  
  <p>This is the scenario that i need to accomplish using Omniauth + Devise.</p>
  
  <p>we have a user named John and he already have accounts in both Google &amp; Facebook with the same email id "John@yopmail.com".</p>
  
  <p>So for the first time John trying to log-in with his Google account, john have successfully logged in this time.</p>
  
  <p>but for the second time john trying to log-in with his facebook account, this time our application redirects john to the devise registration_url , without letting him signing in with his facebook account.</p>
  
  <p>I know why this is hapepnig because devise will internally validates the uniqueness of email.But i am very curious to know that , is there any way to tweak this issue so that we can achieve multiple authentications . Stack-Overflow have done the same very nicely.  </p>
  
  <p>Please help me to find out the solution.</p>
  
  <p>Thank you..</p>