I have added an extra login field to the main wordpress login page. It is a checkbox which must be checked (to accept terms & conditions), otherwise the user cannot log in.

I have taken code from this question which has allowed me to add a custom checkbox to the login. However, trying to modify the code given to validate whether the checkbox has been checked, I cannot get to work.

function check_checkbox($user) {
    $acceptance = $_POST['terms_acceptance'];

    $user = get_user_by('login', $username );

    if( !$user || !isset($acceptance) ){
        remove_action('authenticate', 'wp_authenticate_username_password', 20);

        $user = new WP_Error( 'denied', __("<strong>ERROR</strong>: You're unique identifier was invalid.") );

    return null;
add_filter( 'wp_authenticate_user', 'check_checkbox', 10, 3 );

I have tried the 'authenticate' & 'wp_authenticate_user' filters as shown, but neither have worked for me.

Can anyone tell me what I'm doing wrong?

2 Answers 2


Here's the full working code, put it in functions.php:

function my_added_login_field(){
        <label for="my_extra_field">I agree to the terms<br />
        <input type="checkbox" value="1" class="input" id="my_extra_field" name="my_extra_field_name"/></label>

function check_checkbox($user, $password)
    if( !isset($_POST['my_extra_field_name']) )
        remove_action('authenticate', 'wp_authenticate_username_password', 20);
        $user = new WP_Error( 'denied', __("<strong>ERROR</strong>: Please agree to our terms.") );

    return $user;
add_filter( 'wp_authenticate_user', 'check_checkbox', 10, 3 );

Per the Codex...

add_filter('wp_authenticate_user', 'myplugin_auth_login',10,2);
function myplugin_auth_login ($user, $password) {
     //do any extra validation stuff here
     return $user;

You need to return the $user object. Your function always returns null. This is completely untested but it looks like you just need to use return $user; on the last line instead of return null;

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