AnonymousHandler.cls

@RestResource(urlMapping='/MyRestContextExample/*')
global with sharing class AnonymousHandler {    
    @HttpGet
    global static Account doGet() {
        RestRequest req = RestContext.request;
        RestResponse res = RestContext.response;
        res.addHeader('Access-Control-Allow-Origin', '*');
        String accountId = req.requestURI.substring(req.requestURI.lastIndexOf('/')+1);
        Account result = [SELECT Id, Name, Phone, Website FROM Account WHERE Id = :accountId];
        return result;
    }
 
    @HttpPost
    global static Boolean doPost() {
        RestRequest req = RestContext.request;
        RestResponse res = RestContext.response;
 
        res.addHeader('Access-Control-Allow-Origin', '*');
        return true;
    }
}