Source

File: wp-includes/rest-api/class-wp-rest-server.php

public function check_authentication() {
		/**
		 * Filters REST authentication errors.
		 *
		 * This is used to pass a WP_Error from an authentication method back to
		 * the API.
		 *
		 * Authentication methods should check first if they're being used, as
		 * multiple authentication methods can be enabled on a site (cookies,
		 * HTTP basic auth, OAuth). If the authentication method hooked in is
		 * not actually being attempted, null should be returned to indicate
		 * another authentication method should check instead. Similarly,
		 * callbacks should ensure the value is `null` before checking for
		 * errors.
		 *
		 * A WP_Error instance can be returned if an error occurs, and this should
		 * match the format used by API methods internally (that is, the `status`
		 * data should be used). A callback can return `true` to indicate that
		 * the authentication method was used, and it succeeded.
		 *
		 * @since 4.4.0
		 *
		 * @param WP_Error|null|true $errors WP_Error if authentication error, null if authentication
		 *                                   method wasn't used, true if authentication succeeded.
		 */
		return apply_filters( 'rest_authentication_errors', null );
	}