Close SQL SERVER connection in node.js

I have this code where I open the SQL SERVER connection but I need to close it ... does anyone know how to do it?

router.post('/api/v1/Login', jsonParser, function(req, res){
  if(!req.body)
  return res.sendStatus(400)
  console.log(req.body);

  var UsuarioReg = req.body.user;
  var ContraReg = req.body.pass;
  var token = req.body.token;

  var ip = req.connection.remoteAddress;

  console.log(ip)

  console.log("User: "+UsuarioReg + " Contraseña: "+ContraReg + " Token: "+token)

  var request = new sql.Request();

  var usuario = {
    nombre: UsuarioReg,
    clave : ContraReg
  }
  var jwtClave=ContraReg;
  sql.connect(config, function (err) {

    if (err) {
      console.log("Error code: E0001 \n Validation code: V0001 \n Description: Error trying to connect with the database.")
      console.log(err)
    }else{
      console.log("Conexion satisfactoria")


      try{

        request.query("SELECT * FROM dbo.[Client] WHERE username = '"+UsuarioReg+"'AND pass = '"+ContraReg+"'AND token = '"+token+"'", function (err, recordset) {
          if(err){
          console.log(err); 
          }else{
            if(recordset.rowsAffected > 0){

              console.log("Usuario identificado correctamente")

            var token = jwt.sign({
              usuario : UsuarioReg
            }, jwtClave)

            res.send("Usuario identificado correctamente.")

            }else{
              throw new Error("Error code: E0016 \n Validation code: V0016 \n Description: Alguno de los parametros enviados no es correcto.")
            }
          }
        })
      }catch(err){
        res.send(JSON.stringify("Error while querying database :- "+err))
        console.log("Error while querying database :- "+err)
      }
   }
   });
});