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Description

This action is located inside of wp_signon. In contrast to the wp_login action, it is executed before the WordPress authentication process.

• This action hook is not to be confused with the wp_authenticate pluggable function.

Location

Located in /wp-includes/user.php.

Example

You can use wp_authenticate to use a custom login mechanism before you involve WordPress.

<?php
add_action( 'wp_authenticate' , 'check_custom_authentication' );

function check_custom_authentication ( $username ) {
        global $wpdb;

         if ( ! username_exists( $username ) ) {
        return;
    }
        $userinfo = get_user_by( 'login', $username );
        $property = $wpdb->prefix . 'capabilities';
        $caps = $userinfo->$property;
        foreach ( $caps as $role ) {
              if ( 'special_authenticator' == $role ) {
                    wpExternalLoginProcess( $username, $_POST['pwd'] );
              }
        }
}
?>

You can also use email to authenticate users in WordPress.

<?php
add_action( 'wp_authenticate', 'wp_authenticate_by_email' );
// user name is passed in by reference 
function wp_authenticate_by_email( &$username ) {
    $user = get_user_by( 'email', $username );

    if ( ! $user ) {
        $username = $user->user_login;
    }

}
?>