  We investigate for the first time the potential of angular auto- and
cross-correlation power spectra in identifying sterile neutrino dark matter in
the cosmic X-ray background. We take as reference the performance of the
soon-to-be-launched eROSITA satellite. The main astrophysical background
sources against sterile neutrino decays are active galactic nuclei, galaxies
powered by X-ray binaries, and clusters of galaxies. While sterile neutrino
decays are always subdominant in the auto-correlation power spectra, they can
be efficiently enhanced when cross-correlating with tracers of the dark matter
distribution such as galaxies in the 2MASS catalogues. We show that the planned
four-years eROSITA all-sky survey will provide a large enough photon statistics
to potentially yield very stringent constraints on the decay lifetime, enabling
to firmly test the recently claimed 3.56-keV X-ray line found towards several
clusters and galaxies and its decaying dark matter interpretation. However, we
also show that in order to fully exploit the potential of eROSITA for dark
matter searches, it is vital to overcome the shot-noise limitations inherent to
galaxy catalogues as tracers for the dark matter distribution.
