  How does nonequilibrium activity modify the approach to a glass? This is an
important question, since many experiments reveal the near-glassy nature of the
cell interior, remodelled by activity. However, different simulations of dense
assemblies of active particles, parametrised by a self-propulsion force, $f_0$,
and persistence time, $\tau_p$, appear to make contradictory predictions about
the influence of activity on characteristic features of glass, such as
fragility. This calls for a broad conceptual framework to understand active
glasses; here we extend the Random First-Order Transition (RFOT) theory to a
dense assembly of self-propelled particles. We compute the active contribution
to the configurational entropy using an effective medium approach - that of a
single particle in a caging-potential. This simple active extension of RFOT
provides excellent quantitative fits to existing simulation results. We find
that whereas $f_0$ always inhibits glassiness, the effect of $\tau_p$ is more
subtle and depends on the microscopic details of activity. In doing so, the
theory automatically resolves the apparent contradiction between the simulation
models. The theory also makes several testable predictions, which we verify by
both existing and new simulation data, and should be viewed as a step towards a
more rigorous analytical treatment of active glass.
