Communication between web app and offline application

Current situation:

• Windows application 1 (app1) creates xml file
• app1 runs Windows application 2 (app2)
• app2 reads xml input and does what is needed
• app2 generates new xml file
• app1 handles the resulting xml file

New situation: app1 is rewritten and is now a web application. How can you achieve the communication with the Windows application in a way that is user friendly? Possibly some sort of middleware would be an option?