Use Durable Functions as backend for Static Web App

**Describe the solution you'd like**
I would like my Blazor WASM front end to be able to call an Azure Durable Functions backend when deployed to Static Web Apps. This would allow me to quickly build small robust workflows with a web interface.

I have tried this and get the following error:

`Error in processing api build artifacts: the file 'ConvertToXlf/function.json' has specified an invalid trigger of type 'activityTrigger' and direction ''. Currently, only httpTriggers are supported. Visit https://github.com/Azure/azure-functions-host/wiki/function.json for more information.`

**Describe alternatives you've considered**
Perhaps I can work around this by calling this particular activity function as an external "third party" endpoint from my durable functions workflow but it would be great if there were a simpler option.

Now reading about linking an existing Functions service with my static web app.