Shows how to filter fields in the WPGraphQL Schema to require authentication before resolving.

filter-fields-to-require-auth.php

add_action( 'graphql_register_types', function() {

	/**
	 * Define the Types and their Fields that we want to filter
	 */
	$fields_to_require_auth = [
		'Post' => [
			'author'
		],
		'Comment' => [
			'authorIp',
			'agent'
		],
	];

	/**
	 * Loop through that config
	 */
	foreach ( $fields_to_require_auth as $type_name => $fields_to_filter ) {

		if ( ! empty( $fields_to_filter ) && is_array( $fields_to_filter ) ) {

			/**
			 * Apply a filter to said Type's fields
			 */
			add_filter( 'graphql_' . $type_name . '_fields', function( $fields ) use ( $type_name, $fields_to_filter ) {

				/**
				 * Loop through each of the fields we want to filter for this Type
				 */
				foreach ( $fields_to_filter as $field_name ) {

					/**
					 * The registry normalizes all keys to lowercase, so we make our $field_name lowercase here too
					 */
					$field_key = strtolower( $field_name );

					/**
					 * Make sure the field exists in the registry (it could have been removed by another plugin)
					 */
					if ( isset( $fields[ $field_key ] ) ) {

						/**
						 * If the request is not authenticated (no current user is set), override the resolver for the field to throw
						 * a UserError
						 *
						 * Change this to whatever condition you want
						 */
						if ( ! get_current_user_id() ) {
							$fields[ $field_key ]['resolve'] = function ( $root, $args, $context, $info ) use ( $type_name, $field_name ) {
								throw new \GraphQL\Error\UserError( __( sprintf( 'You do not have access to view the "%1$s" Field on the %2$s Type', $field_name, $type_name ), 'wp-graphql' ) );
							};
						}
					}
				}

				/**
				 * Return the fields to the filter.
				 */
				return $fields;
			} );
		}
	}

} );