Ember.js LDAP authentication

I'm haveing project with frontend in Ember.js and backend in Symfony2. Basic authentication is thru login form. form sends username and password to symfony2 fosuser bundle.

Now i want users to be authenticated also by Active Directory. I have upgraded my backend to use also FR3LDAP bundle. There i can use AD login and password and new user is created if not exists. All works fine.

Now i need to make ember frontend workable. Login form cannot authenticate LDAP data because we are not storing LDAP users pass in DB.

How should i modify my ember app to automatically check if user is logged in AD and authenticate him without using password? im using simple-auth-oauth2.