The answer from Jack Zeng was close, but (at this point in time) you need auditingSettings to point to blob storage, since security alerting doesn't work with table storage. So add the following auditingSettings and securityAlertPolicies as child resources of the Microsoft.Sql/servers resource.
{
"$schema": "https://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
"contentVersion": "1.0.0.0",
"parameters": {},
"variables": {},
"resources": [
{
"name": "[parameters('sqlserverName')]",
"type": "Microsoft.Sql/servers",
"location": "[resourceGroup().location]",
"apiVersion": "2014-04-01-preview",
"properties": {},
"resources": [
{
"apiVersion": "2015-05-01-preview",
"type": "auditingSettings",
"name": "Default",
"dependsOn": [
"[parameters('sqlserverName')]",
"[concat('Microsoft.Storage/storageAccounts/', parameters('storageAccountName'))]"
],
"properties": {
"State": "Enabled",
"storageEndpoint": "[concat('https://', parameters('storageAccountName'), '.blob.core.windows.net/')]",
"storageAccountAccessKey": "[listKeys(resourceId('Microsoft.Storage/storageAccounts', parameters('storageAccountName')), providers('Microsoft.Storage', 'storageAccounts').apiVersions[0]).keys[0].value]",
"storageAccountSubscriptionId": "[subscription().subscriptionId]",
"eventTypesToAudit": "All"
}
},
{
"apiVersion": "2015-05-01-preview",
"type": "securityAlertPolicies",
"name": "DefaultSecurityAlert",
"dependsOn": [
"[parameters('sqlserverName')]",
"[concat('Microsoft.Storage/storageAccounts/', parameters('storageAccountName'))]",
"[concat('Microsoft.Sql/servers/', parameters('sqlserverName'), '/auditingSettings/Default')]"
],
"properties": {
"state": "Enabled",
"disabledAlerts": "",
"emailAddresses": "[parameters('securityAlertPolicyEmails')]",
"emailAccountAdmins": "Enabled",
"retentionDays": "10",
"storageEndpoint": "[concat('https://', parameters('storageAccountName'), '.blob.core.windows.net/')]",
"storageAccountAccessKey": "[listKeys(resourceId('Microsoft.Storage/storageAccounts', parameters('storageAccountName')), providers('Microsoft.Storage', 'storageAccounts').apiVersions[0]).keys[0].value]"
}
}
]
}
]
}
Sources:
The blob storage auditing config is from here: https://blogs.msdn.microsoft.com/azuresqldbsupport/2017/01/11/arm-template-turning-on-blob-auditing/
The threat detection resource config is from here (note that the storage auditing config from this example didn't work for me): https://blogs.msdn.microsoft.com/azuresqldbsupport/2017/01/11/arm-template-to-deploy-server-with-auditing-and-threat-detection-turned-on/