wp_authenticate_cookie( WP_User|WP_Error|null $user, string $username, string $password )

Source

File: wp-includes/user.php

function wp_authenticate_cookie( $user, $username, $password ) {
	if ( $user instanceof WP_User ) {
		return $user;
	}

	if ( empty( $username ) && empty( $password ) ) {
		$user_id = wp_validate_auth_cookie();
		if ( $user_id ) {
			return new WP_User( $user_id );
		}

		global $auth_secure_cookie;

		if ( $auth_secure_cookie ) {
			$auth_cookie = SECURE_AUTH_COOKIE;
		} else {
			$auth_cookie = AUTH_COOKIE;
		}

		if ( ! empty( $_COOKIE[ $auth_cookie ] ) ) {
			return new WP_Error( 'expired_session', __( 'Please log in again.' ) );
		}

		// If the cookie is not set, be silent.
	}

	return $user;
}