Counting Black Hole Microstates at Future Null Infinity

We propose a black hole microstate counting method based on the canonical quantization of the asymptotic symmetries of a two-dimensional dilaton-gravity system at future null infinity. This dilaton-gravity is obtained from the s-wave reduction of an $N$-dimensional Einstein gravity over a generic asymptotically flat black hole solution. We show that a Cardy-type formula leads to the Bekenstein-Hawking entropy. In this scenario, the quantized bulk degrees of freedom act as a source for the dual field theory operators living at future null infinity that are soft gravitons of the higher dimensional system, up to some gauge fixing.