check_password_reset_key( string $key, string $login )

function check_password_reset_key($key, $login) {
	global $wpdb, $wp_hasher;

	$key = preg_replace('/[^a-z0-9]/i', '', $key);

	if ( empty( $key ) || !is_string( $key ) )
		return new WP_Error('invalid_key', __('Invalid key'));

	if ( empty($login) || !is_string($login) )
		return new WP_Error('invalid_key', __('Invalid key'));

	$row = $wpdb->get_row( $wpdb->prepare( "SELECT ID, user_activation_key FROM $wpdb->users WHERE user_login = %s", $login ) );
	if ( ! $row )
		return new WP_Error('invalid_key', __('Invalid key'));

	if ( empty( $wp_hasher ) ) {
		require_once ABSPATH . WPINC . '/class-phpass.php';
		$wp_hasher = new PasswordHash( 8, true );
	}

	/**
	 * Filters the expiration time of password reset keys.
	 *
	 * @since WP-4.3.0
	 *
	 * @param int $expiration The expiration time in seconds.
	 */
	$expiration_duration = apply_filters( 'password_reset_expiration', DAY_IN_SECONDS );

	if ( false !== strpos( $row->user_activation_key, ':' ) ) {
		list( $pass_request_time, $pass_key ) = explode( ':', $row->user_activation_key, 2 );
		$expiration_time = $pass_request_time + $expiration_duration;
	} else {
		$pass_key = $row->user_activation_key;
		$expiration_time = false;
	}

	if ( ! $pass_key ) {
		return new WP_Error( 'invalid_key', __( 'Invalid key' ) );
	}

	$hash_is_correct = $wp_hasher->CheckPassword( $key, $pass_key );

	if ( $hash_is_correct && $expiration_time && time() < $expiration_time ) {
		return get_userdata( $row->ID );
	} elseif ( $hash_is_correct && $expiration_time ) {
		// Key has an expiration time that's passed
		return new WP_Error( 'expired_key', __( 'Invalid key' ) );
	}

	if ( hash_equals( $row->user_activation_key, $key ) || ( $hash_is_correct && ! $expiration_time ) ) {
		$return = new WP_Error( 'expired_key', __( 'Invalid key' ) );
		$user_id = $row->ID;

		/**
		 * Filters the return value of check_password_reset_key() when an
		 * old-style key is used.
		 *
		 * @since WP-3.7.0 Previously plain-text keys were stored in the database.
		 * @since WP-4.3.0 Previously key hashes were stored without an expiration time.
		 *
		 * @param WP_Error $return  A WP_Error object denoting an expired key.
		 *                          Return a WP_User object to validate the key.
		 * @param int      $user_id The matched user ID.
		 */
		return apply_filters( 'password_reset_key_expired', $return, $user_id );
	}

	return new WP_Error( 'invalid_key', __( 'Invalid key' ) );
}