Sliding boundary conditions in Solid Mechanics

Hi!

I am trying to model a sliding boundary condition between to elastic bodies.
By sliding condition here I mean, that the DIFFERENCE between the displacement fileds should always be zero in the normal direction between two bodies i sliding contact.
I understand that I need to buid an assemby and create a contact pair between two bodies. And then apply a contact condition. But there is no such contact condition, so far I know. Is there a way to create your own condition or modify the existing one?

Another easier way is to prescribe the displacement on the boundary as:

u_source * nX = u_destination * nX
v_souce * nY = v_destination * nY

But I cannot find the variables for diplacement on source boundary and destination boundary.

I appreciate any help I could get.