Switch Authentication on or off depending on IP Address

I have a client who has one fixed location with a fixed IP address.

The majority of users will be at this location and I would like them only to need a password to access the application when at this site and accessing through this IP Address

For users off site I would like them to use MS authentication or some other form of authentication..

Is this functionality available yet without custom coding?
If it isn't how difficult is the coding?