[DougWebb]

It depends on where the link is. If it's in a web page and the user's browser supported any valid method in forms, you could use a form with method="DELETE" and action="uri for user's subscription", with a submit button styled to look like a link. For browsers that don't support the DELETE method in forms, you can add a hidden input _method=DELETE which is the semi-standard workaround for incomplete browser support. (Your service has to look for _method when it gets a POST and react accordingly.)

If the link is in an email, a form probably won't work. Email clients are still worse than browsers when it comes to styling buttons to look like links. In that case, you can use a real link, but add the _method=DELETE to the url parameters. You service can then look for _method on GET requests too. But it's bad and hacky to change a GET into a DELETE, so you really should just use the link to display a web page, then delete with a DELETE or POST from there. That's what most unsubscribe links in emails do anyway.