Validating Username and Password in Keycloak

I am trying to validate a users username and password from keycloak backend because I have a custom authentication form. I was using the below code to validate the user, which is working as expected.

private UserModel getUserByUserNameAndPassword(AuthenticationFlowContext context, String username,
        String password) {
    RealmModel realm = context.getRealm();
    UserModel user = context.getSession().users().getUserByUsername(realm, username);
    if (user != null) {
        context.setUser(user);
        context.success();
    }
    return user;
}

But I cant validate the password of that user. Can somebody help me to use the password for validating the user.

Thanks in advance.

Here is the solution worked for me. I used validatePassword function in the AbstractUsernameFormAuthenticator class.

My inputData from form parameter provide username and password.

private UserModel getUserByUserNameAndPassword(AuthenticationFlowContext context, String username) {
    RealmModel realm = context.getRealm();
    UserModel user = context.getSession().users().getUserByUsername(realm, username);
    MultivaluedMap<String, String> inputData = context.getHttpRequest().getDecodedFormParameters();
    boolean shouldClearUserFromCtxAfterBadPassword = !isUserAlreadySetBeforeUsernamePasswordAuth(context);

    if (user != null
            && validatePassword(context, user, inputData, shouldClearUserFromCtxAfterBadPassword)) {
        return user;
    } else {
        return null;
    }
}