  Proton energization at magnetic discontinuities generated by phase-steepened
fronts of parallel propagating, large-amplitude Alfv\'enic fluctuation is
studied using hybrid simulations. We find that dispersive effects yield to the
collapse of the wave via phase steepening and the subsequent generation of
compressible fluctuations that mediate an efficient local energy transfer from
the wave to the protons. Proton scattering at the steepened edges causes
non-adiabatic proton perpendicular heating. Furthermore, the parallel electric
field at the propagating fronts mediates the acceleration of protons along the
mean field. A steady-state is achieved where proton distribution function
displays a field-aligned beam at the Alfv\'en speed, and compressible
fluctuations are largely damped. We discuss the implications of our results in
the context of Alfv\'enic solar wind.
