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The authenticate filter hook is used to perform additional validation/authentication any time a user logs in to WordPress.

The wp_authenticate_user filter can also be used if you want to perform any additional validation after WordPress’s basic validation, but before a user is logged in.

The default authenticate filters in /wp-includes/default-filters.php

add_filter( 'authenticate', 'wp_authenticate_username_password',  20, 3 );
add_filter( 'authenticate', 'wp_authenticate_email_password',     20, 3 );
add_filter( 'authenticate', 'wp_authenticate_spam_check',         99    );