cert-update.json

{
    "$schema": "https://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
    "contentVersion": "1.0.0.0",
    "parameters": {
       "webAppName": {
	  "type": "string"
       },
       "customDomain": {
	  "type": "string"
       },
       "location": {
	  "type": "string"
       },
       "certThumbprint": {
	  "type": "string"
       }
    },
    "resources": [
	{
       	  "type": "Microsoft.Web/sites/hostnameBindings",
          "name": "[concat(parameters('webAppName'), '/', parameters('customDomain'))]",
          "apiVersion": "2019-04-01",
          "location": "[parameters('location')]",
          "properties": {
             "sslState": "SniEnabled",
             "thumbprint": "[parameters('certThumbprint')]"
          }
        }
    ]
}