  We investigate gravitational microlensing signals produced by a spatially
extended object transiting in front of a finite-sized source star. The most
interesting features arise for lens and source sizes comparable to the Einstein
radius of the setup. Using this information, we obtain constraints from the
Subaru-HSC survey of M31 on the dark matter populations of NFW subhalos and
boson stars of asteroid to Earth masses. These lens profiles capture the
qualitative behavior of a wide range of dark matter substructures. We find that
deviations from constraints on point-like lenses (e.g. primordial black holes
and MACHOs) become visible for lenses of radius 0.1 $R_\odot$ and larger, with
the upper bound on lens masses weakening with increasing lens size.
