[auth] Implemented fetchProvidersForEmail

lib/modules/auth/index.js

@@ -156,6 +156,14 @@ export default class Auth extends Base {
     return this._interceptUserValue(FirebaseAuth.getCurrentUser());
   }
 
+  /**
+   * Returns a list of authentication providers that can be used to sign in a given user (identified by its main email address).
+   * @return {Promise}
+   */
+  fetchProvidersForEmail(email: string): Promise<Object> {
+    return FirebaseAuth.fetchProvidersForEmail(email);
+  }
+
   /**
    * Get the currently signed in user
    * @return {Promise}