Hello we are developing a hydra render delegate of our renderer, which will be used to render images from houdini solaris.
Currently, the basic AOVs (customized ones, e.g., direct lighting & indirect lighting) can be successfully copied and displayed in houdini, however we want to export cryptomatte buffers while cannot find any interface of this feature. Could anyone please provide some hint for example which USD or houdini API I should check? Thanks.

This is discussed a little bit in https://www.sidefx.com/docs/hdk/_h_d_k__u_s_d_hydra.html#HDK_USDHydraHusk [www.sidefx.com]
Hopefully that helps you get started.

The interface has changed for the next version of Houdini though so that there are no dependencies on the Houdini USD Bridge.