Is there any derivation of Wald's entropy for Kerr Black Holes?
We know that Wald had shown that one can derive the entropy for Schwarzschild black holes via conserved charge. The functional differentiation on Wald's entropy is on r and t direction however. Please see this paper's Eq. (6) for neat form of Wald's entropy around Schwarzschild background.
However Kerr metric has off diagonal terms. I wonder if there is any Wald's approach to derive the entropy for Kerr black holes in similar manner? Can one use Sen's entropy functional? or any other approach?