Modifies the "authors" included in the REST response for /wp/v2/users/?who=authors

rest-authors-query.php

<?php 

add_filter( 'rest_user_query', 'my_custom_rest_authors', 25, 2 );
/**
 * Modifies the "authors" included in the REST response for /wp/v2/users/?who=authors
 *
 * @param  array 	$args    	Query args
 * @param  object 	$request 	REST request
 *
 * @return array
 */
function my_custom_rest_authors( $args, $request ) {
	
	if ( ! empty( $request['who'] ) && 'authors' === $request['who'] ) {

		// Customize which roles are considered authors
		$rest_author_roles = array();

		// Get registered roles
		$roles = wp_roles();

		// Check each role for the edit_posts capability
		// Change this as needed
		foreach ( $roles->roles as $key => $r ) {
			$role = $roles->get_role( $key );
			if ( $role->has_cap( 'edit_posts' ) ) {
				$rest_author_roles[] = $key;
			}
		}
		
		$args['role__in'] = array_merge( ! empty( $args['role__in'] ) ? $args['role__in'] : array(), $rest_author_roles );
		$args['who'] = '';
	}

	return $args;
}