ARM Template - Automate Azure Function Event Grid Subscription

Presently using ARM I can automate the creation of an Azure Function Subscriber that has a HTTP trigger.

"properties": {
"destination": {
"endpointType": "WebHook",
"properties": {
"endpointUrl": "[listsecrets(resourceId('Microsoft.Web/sites/functions', parameters('azurefunctions_name'), parameters('azurefunctions_loadTcsItemSubscription')),'2015-08-01').trigger_url]"
}
},
"filter": {
"includedEventTypes": [
"All"
]
}
},

I am however unable to do the same for an Azure Function Event Grid trigger, there seems to be no way of accessing the system key.

Many Thanks

No files, tests, or entry points are identified. Start by investigating how ARM creates Azure Function Event Grid subscriptions and how the system key is exposed for Event Grid triggers; done when the subscription can be automated through ARM with the required function authentication.

Written by the indexing model from the issue text.