fix: migrate ExecCredential API from v1beta1 to v1 (#641)

client.authentication.k8s.io/v1beta1 has been deprecated and removed
in recent Kubernetes versions. Update to v1 which has an identical
response structure.

Author: wasaga

cmd/pomerium-cli/kubernetes.go

@@ -115,7 +115,7 @@ func parseToken(rawjwt string) (*ExecCredential, error) {
 
 	return &ExecCredential{
 		TypeMeta: TypeMeta{
-			APIVersion: "client.authentication.k8s.io/v1beta1",
+			APIVersion: "client.authentication.k8s.io/v1",
 			Kind:       "ExecCredential",
 		},
 		Status: &ExecCredentialStatus{