TaxPro GST Lib
User guide (Under Construction)
  • Digital Signing GST and ITR eReturns using Signer.Digital Chrome Extension
Digital Signing GST and ITR eReturns using Signer.Digital Browser Extension
Note: Signer.Digital Browser Extension is completely free for unlimited uses.

More JavaScript API in Signer.Digital Browser Extension may be referred at this Stacks Overflow Answer
Sample JavaScript and Server side pseudo code code to sign GST or IT return using Signer.Digital Browser Extension:
function getSignature(hash){
       //Sign GSTR Return Hash using Signer.Digital Chrome Extension
       //This method returns CMS (PKCS7) Signature
       SignerDigital.signGstHash(hash, CertThumbprint = "")
           //send signature to return filing server
           //send error to server and/or report error to user
//For Income Tax Return signing use method:
//This method returns SHA256 Signature
SignerDigital.signITHash(hash, PAN, CertThumbprint = "")
Parameter PAN is optional. If value given, certificate with given PAN will be selected silently from the certificate store without opening Certificate Selection dialog.