Calculate SHA256 Digest Of PDDataBuffer in PSSigAuthenticateProc Callback

I have created a third party adobe signature plugin to sign the document and i am using Adobe PDF Default method to verify the signature.

I need to calculate the digest of a pdf file by using SHA256 Digest Method for signing the pdf document.

I am able to achieve it successfully by calculating the Digest of the PDDataBuffer in PSSigGetSigValueProc callback. But i need to calculate the digest in PSSigAuthenticateProc callback as per my business logic.

Is there something to achieve the correct SHA256 Digest of the PDDataBuffer in the PSSigAuthenticateProc callback to sign and validate the Signature.

Regards,
Vivek Kumar