I am given the next pseudometric:

$$
ds^2=dt^2-\frac{r^2+a^2 \cos^2 \theta}{r^2+a^2}dr^2-(r^2+a^2)\sin^2 \theta d\phi^2-(r^2+a^2\cos^2 \theta)d\theta^2.
$$

How to find the isometry group for such space-time? Mostly I'm interested in a general approach.