public function check_authentication() {

		// allow plugins to remove default authentication or add their own authentication
		$user = apply_filters( 'woocommerce_api_check_authentication', null, $this );

		if ( is_a( $user, 'WP_User' ) ) {

			// API requests run under the context of the authenticated user
			wp_set_current_user( $user->ID );

		} elseif ( ! is_wp_error( $user ) ) {

			// WP_Errors are handled in serve_request()
			$user = new WP_Error( 'woocommerce_api_authentication_error', __( 'Invalid authentication method', 'woocommerce' ), array( 'code' => 500 ) );

		}

		return $user;
	}