How to deploy applications to k8s using bitbucket pipelines?
You need to separate your daily authentication method of the CD authentication.

You should start understanding the different methods that K8S offers https://kubernetes.io/docs/admin/authentication/

On the other hand if you use some cloud solution like GCP you can benefit of the service account that the platform puts in all your instances, setting the right permissions to a service account allow you to to controll any cluster inside your project like in your local machine.