Duplicate emails with Ionic Auth services


We are developing ionic 2 app using the authentication with Ionic Auth service. We will allow our customers to login using basic, Facebook, Google and Linkedin authentications.

I implemented all these 4 auth providers successfully. The problem is Ionic Auth Service is allowing to have the same email multiple times (when this email email is used in every authentication provider)

We want to prevent users to have multiple accounts (using fb, google, etc…) with the same email.

Furthermore, if user has already been registered using google with user@gmail.com and he tried to login/register with the same email in Facebook, we want to popup a message that says we have already an account with this email register using google.

How can we implement that? Thanks a lot