Multi-tenant help

I have developed a multi-tenant SaaS app using meteor for schools called STPPEIFY. It uses a combination of userId authorization and URL parameters to determine the School of the userId. From the single core I create mobile specific to the School for Android. Everything good so far.

Each of the school wants to use their own domain name to access the application. This also works fine. I use nginx to redirect to the core application.

Now I am trying to see if we can incorporate oAuth for Facebook, Google, Twitter.

Here I am running into problems. If I use a URL(other than core) that is redirected to my core Meteor app the browser gives error when I use the oAuth process - 'cannot be from different origins and ’ for Web App alone (Meteor root_url is, on mobile it works fine. I know I am doing something wrong with my design. I am sure somebody knows how to solve this or has faced similar issue. Any pointers would be of great help.

Till that time I am forced not to use oAuth functionality or just use core application URL to access oAuth functionality.

Thanks in advance for any pointers.