var ENCODED_USERNAME = '098f6bcd4621d373cade4e832627b4f6',
    ENCODED_PASSWORD = '5f4dcc3b5aa765d61d8327deb882cf99';

var usernameField = document.getElementById('username'),
    passwordField = document.getElementById('password'),
    submitButton = document.getElementById('submit');

submitButton.onclick = function() {
    var username = usernameField.value,
        password = passwordField.value;

    var usernameHash = hex_md5(username),
        passwordHash = hex_md5(password);

    if(usernameHash === ENCODED_USERNAME &&
       passwordHash === ENCODED_PASSWORD)
    {
        alert('Correct!');
    } else {
        alert('Incorrect!');
    }
}

/* N.B.:
 * This is a demonstration/proof of concept.
 * Of course, for multiple reasons, it is not secure enough to be used in production.
 */