  We report on a self-consistent microscopic study of the DC Josephson effect
in $SINIS$ junctions where screened dipole layers at the $SN$ interfaces
generate a double-barrier multilayered $SIN$ structure. Our approach starts
from a microscopic Hamiltonian defined on a simple cubic lattice, with an
attractive Hubbard term accounting for the short coherence length
superconducting order in the semi-infinite leads, and a spatially extended
charge distribution (screened dipole layer) induced by the difference in Fermi
energies of the superconductor $S$ and the clean normal metal interlayer $N$.
By employing the temperature Green function technique, in a continued fraction
representation, the influence of such spatially inhomogeneous barriers on the
proximity effect, current-phase relation, critical supercurrent and normal
state junction resistance, is investigated for different normal interlayer
thicknesses and barrier heights. These results are of relevance for high-$T_c$
grain boundary junctions, and also reveal one of the mechanisms that can lead
to low critical currents of apparently ballistic $SNS$ junctions while
increasing its normal state resistance in a much weaker fashion. When the $N$
region is a doped semiconductor, we find a substantial change in the dipole
layer (generated by a small Fermi level mismatch) upon crossing the
superconducting critical temperature, which is a new signature of proximity
effect and might be related to recent Raman studies in Nb/InAs bilayers.
