Use the WordPress REST API directly in PHP without actually making an HTTP request.

wp-internal-rest-request.php

<?php

function wpscholar_rest_get_request( $route, array $params = [] ) {
	$request = new WP_REST_Request( 'GET', $route );
	$request->set_query_params( $params );
	$response = rest_do_request( $request );

	return rest_get_server()->response_to_data( $response, false );
}

function wpscholar_rest_post_request( $route, array $params = [] ) {
	$request = new WP_REST_Request( 'POST', $route );
	$request->set_body_params( $params );
	$response = rest_do_request( $request );

	return rest_get_server()->response_to_data( $response, false );
}