  We apply a recently presented BRST procedure to construct the Largangian
cubic vertex of higher-spin gauge field triplets interacting with massive free
scalars. In flat space, the spin-s triplet propagates the series of irreducible
spin-s, s-2,..,0/1 modes which couple independently to corresponding conserved
currents constructed from the scalars. The simple covariantization of the flat
space result is not enough in AdS, as new interaction vertices appear. We
present in detail the cases of spin-2 and spin-3 triplets coupled to scalars.
Restricting to a single irreducible spin-s mode we uncover previously obtained
results. We also present an alternative derivation of the lower spin results
based on the idea that higher-spin gauge fields arise from the gauging of
higher derivative symmetries of free matter Lagrangians. Our results can be
readily applied to holographic studies of higher-spin gauge theories.
