  The circumgalactic medium (CGM) plays a crucial role in galaxy evolution as
it fuels star formation, retains metals ejected from the galaxies, and hosts
gas flows in and out of galaxies. For Milky Way-type and more massive galaxies,
the bulk of the CGM is in hot phases best accessible at X-ray wavelengths.
However, our understanding of the CGM remains largely unconstrained due to its
tenuous nature. A promising way to probe the CGM is via X-ray absorption
studies. Traditional absorption studies utilize bright background quasars, but
this method probes the CGM in a pencil beam, and, due to the rarity of bright
quasars, the galaxy population available for study is limited. Large-area, high
spectral resolution X-ray microcalorimeters offer a new approach to exploring
the CGM in emission and absorption. Here, we demonstrate that the cumulative
X-ray emission from cosmic X-ray background sources can probe the CGM in
absorption. We construct column density maps of major X-ray ions from the
Magneticum simulation and build realistic mock images of nine galaxies to
explore the detectability of X-ray absorption lines arising from the
large-scale CGM. We conclude that the OVII absorption line is detectable around
individual massive galaxies at the $3\sigma-6\sigma$ confidence level. For
Milky Way-type galaxies, the OVII and OVIII absorption lines are detectable at
the $\sim\,6\sigma$ and $\sim\,3\sigma$ levels even beyond the virial radius
when co-adding data from multiple galaxies. This approach complements emission
studies, does not require additional exposures, and will allow probing of the
baryon budget and the CGM at the largest scales.
