internal/arms/API.SB.ConnectionString.json

{
    "type": "Microsoft.Web/connections",
    "apiVersion": "2018-07-01-preview",
    "name": "##NAME##",
    "location": "[parameters('logicAppLocation')]",
    "properties": {
        "api": {
            "id": "[subscriptionResourceId('Microsoft.Web/locations/managedApis', parameters('logicAppLocation'), 'servicebus')]"
        },
        "displayName": "##NAME##",
        "parameterValues": {
            "connectionString": "[listKeys(resourceId('##SUSCRIPTIONID##', '##RESOURCEGROUPNAME##', 'Microsoft.ServiceBus/namespaces/authorizationRules', '##NAMESPACE##', '##KEYNAME##'), providers('Microsoft.ServiceBus', 'namespaces').apiVersions[0]).primaryConnectionString]"
        }
    }
}