So far, we have made use of the out-of-the-box web services provided in the SharePoint. There are situations where SharePoint could be acting as a data store providing your business data to external applications. These applications requesting data may need to provide information on having a valid subscription or license before accessing the data. The out-of-the-box web services will not provide you a way to verify this information before allowing access. There may also be a scenario where you may want to strip out confidential information from the list before passing the data to these external applications. In these scenarios, you can create your own custom web service which could validate the credentials, or strip out the confidential data before passing the information to these external applications.
In this recipe, we will create a custom SharePoint WCF service which returns us the ubiquitous string Hello World.