how to map XML/Soap Signatures Blocks to JSON String

Hi Team, We have SOAP/XML based implementation in place, and want to move to the REST APIs. During the process,some module in our system would to prepare the Approval Blocks ( place holder for signatures) and same document is handover to other module which sends this file to Silanis for E-Signing process. I am trying to use the same document which has signature blocks ( set by other module). But Believe with REST API implementation, Signature Blocks need to be defined as part of JSON request payload ( Approvals- Fields..... ) The issue i am facing , I am not able to get the co-ordinates of the Signature blocks prepared using SOAP/XML based integration. Is there a way in which I can identity the signature Blocks in java Code ( REST APIs) and map them to JSON to be inline with file that is received. Thanks in advance. Thanks, Srikanth