app.post('/authenticate_user', function(req, res){
    var mail = req.body.Mail;
    var password = req.body.Password;
    res.setHeader("Cache-Control", "private, no-cache, no-store, must-revalidate, max-age=0");
    var isValid=authenticate_user(mail, password);
    console.log("isValid-->"+isValid);

    res.json(isValid);
});
var authenticate_user=function(mail, password){
    var query = user_details.find({'Mail': mail});
    query.exec( function(err, docs){
        if (docs.length==0) {
            return false;
        }
        else{
            return(docs[0].Password==password);
        }
    });