Any ideas on login using Digital Signature PKCS I am curious to know about possibility to login into web application just by identifying the user based on digital signature in usb token.

any reference in this direction?
Web application, using modern browsers, may access user's Certificate Store or USB Token or Smartcard (through Certificate Store using CSP in token driver) through Browser Extension.

Methods like java applets, Active X, etc are being phased out from the new Modern Browser offerings. Recently much is being talked about WebCrypto API but as of now, WebCrypto API does not provide access to (Windows) or any other Key stores or local crypto USB/Smartcard device.

For Authentication from Browser using Digital Signature, one such free Chrome extension available is Signer.Digital chrome extension. Local system (host running behind the chrome browser on windows) setup may be downloaded from https://download.cnet.com/Signer-Digital-Chrome-Extension/3000-33362_4-78042540.html
 Installing this host and restarting Chrome will automatically add Signer.Digital Chrome Extension

The actual working of this extension is illustrated here

Javascript to call method from extension:

To Register Certificate on Server:

//Get Selected Certificate Information 
SignerDigital.getSelectedCertificate()
    .then(
        function (CertInfo) {        
    //Success returns Certificate Subject and Thumbprint
        },
            function (errmsg) {
                //Send errmsg to server or display the result in browser.
              }
     );


To authenticate or Login using Digital Signature:

SignerDigital.signAuthToken(authToken, "SHA-256")       //or "SHA256"
    .then(
        function (SignData) {        //Success returns Signed Auth Token
        },
            function (errmsg) {
                //Send errmsg to server or display the result in browser.
              }
     );


To sign PDF:

    //Calculate Sign for the Hash by Calling function from Extension SignerDigital
    SignerDigital.signPdfHash(hash, $("#CertThumbPrint").val(), "SHA-256")      //or "SHA256"
     .then(
            function (signDataResp) {
              //Send signDataResp to Server
        },
            function (errmsg) {
                //Send errmsg to server or display the result in browser.
              }
     );


If Failed: returns error msg starting with "SDHost Error:"

Disclosure: I work for CISPL which offers Signer.Digital Browser Extension