code: function(c, signature) {
      if(c.session.certificateRequest !== null &&
        c.session.clientCertificate !== null) {
        // create certificate verify message
        tls.queue(c, tls.createRecord(c, {
          type: tls.ContentType.handshake,
          data: tls.createCertificateVerify(c, signature)
        }));
      }
  
      // create change cipher spec message
      tls.queue(c, tls.createRecord(c, {
        type: tls.ContentType.change_cipher_spec,
        data: tls.createChangeCipherSpec()
      }));
  
      // create pending state
      c.state.pending = tls.createConnectionState(c);
  
      // change current write state to pending write state
      c.state.current.write = c.state.pending.write;
  
      // create finished message
      tls.queue(c, tls.createRecord(c, {
        type: tls.ContentType.handshake,
        data: tls.createFinished(c)
      }));
  
      // expect a server ChangeCipherSpec message next
      c.expect = SCC;
  
      // send records
      tls.flush(c);
  
      // continue
      c.process();
    }
docs: create callback to handle client signature (for client-certs)