Authenticating Sharepoint 2013 OnPrem through a remote website using Javascript

Hi All,

Can you please share ways of authenticating SharePoint 2013(onprem ) through JavaScript from a  asp.net website(non-SharePoint) hosted remotely.

The SP 2013 onprem can be hosted by our customers using any security schemes(may be custom providers as well)

Scenario- 

1. In case both Sp and remote non-SP website use Ad Integrated windows authentication , we can assume that they have similar set of users.

2. If not 1, SharePoint can be configured using any authentication scheme(FBA, Claims etc.)

3. The data access from asp .net website to SharePoint is made through browser(client side)

While in 1, I am assuming pass-through authentication should work. Need your assistance with the second scenario above .

Thanks

Sonal.