Explicit construction of a Chern-Moser connection for CR manifolds of   codimension two
  In the present paper we suggest an explicit construction of a Cartan connection for an elliptic or hyperbolic CR manifold M of dimension six and codimension two, i.e. a pair (P, w), consisting of a principal bundle P over M and of a Cartan connection form w on P, satisfying the following property: the (local) CR transformations of M are in one to one correspondence with the (local) automorphisms of P which preserve w. For any point x in M, this construction determines an explicit immersion of the stability subalgebra Lie(aut(M)_x) into the Lie algebra Lie(H) of the structure group H of P. 
Gerd Schmalz and Andrea Spiro