Updating an existing record through an email link click

My application tracks tasks assigned to individuals. It sends a nightly digest email with each individual's open tasks. I'd like to include in that email a simple mechanism for the user to click a link and mark the task as done. Ideally they'd not have to see a Zoho form; e.g. the link would be a call to a web service, with parameters preset with the task ID. The receiving service would simply select the task by that ID and update the value of the field called "Complete."

If the only way to do it is to display a stateless form to the user, that's acceptable too, but not ideal.

Can someone point me in the right direction on how to implement this? Is there a way to expose a non visual web service that receives input and processes it? I see Zoho has an API but it appears to be more for the Zoho apps - correct?