The new Key Management API of Azure Functions has gone live. Its possible via the following ARM Script. Also check this Github issue
"variables": {
"functionAppId": "[concat(parameters('functionAppResourceGroup'),'/providers/Microsoft.Web/sites/', parameters('functionAppName'))]"
},
"resources": [
{
"type": "Microsoft.KeyVault/vaults/secrets",
"name": "[concat(parameters('keyVaultName'),'/', parameters('functionAppName'))]",
"apiVersion": "2015-06-01",
"properties": {
"contentType": "text/plain",
"value": "[listkeys(concat(variables('functionAppId'), '/host/default/'),'2016-08-01').functionKeys.default]"
},
"dependsOn": []
}
]