Kubernetes has native integration with Microsoft Azure, for that a Kubernetes installation on Azure will require API access to manage the cluster’s resources in Azure (for example, to create a cloud load balancer). Some installations of Kubernetes on Azure rely on a shared file on the node that contains credentials to the Azure API under /etc/kubernetes/azure.json. A Pod with access to this file may become a gateway for an attacker to control your Azure environment.
The better solution would be to use Azure Managed Identities instead of a static SPN. However this functionality is not mature yet, and is currently available in alpha stage only for aks-engine (non-managed Kubernetes).
You can update or rotate the cluster SPN credentials, in order to prevent leaked credentials to persist over time.