Coupling of matter to supergravity from the rheonomic symmetry point of view and the origin of the auxiliary fields

We write a first-order action for the Wess-Zumino supermultiplet regarding it as a 0-form on the graded Poincaré supergroup manifold. The standard supersymmetry transformations are reproduced by the rheonomic symmetry mechanism. When this action is coupled to the geometrical action of supergravity on the group manifold, the same rheonomic symmetry mechanism automatically generates the so-called minimal set of auxiliary fields.