expose KubeConfigFromREST in envtest

Signed-off-by: Tiger Kaovilai <tkaovila@redhat.com>

pkg/envtest/client/client.go

@@ -0,0 +1,60 @@
+package client
+
+import (
+	"fmt"
+	"net/url"
+
+	"k8s.io/client-go/rest"
+	"k8s.io/client-go/tools/clientcmd"
+	kcapi "k8s.io/client-go/tools/clientcmd/api"
+)
+
+const (
+	envtestName = "envtest"
+)
+
+// KubeConfigFromREST reverse-engineers a kubeconfig file from a rest.Config.
+// The options are tailored towards the rest.Configs we generate, so they're
+// not broadly applicable.
+//
+// This is not intended to be exposed outside envtest for the above reasons.
+func KubeConfigFromREST(cfg *rest.Config) ([]byte, error) {
+	kubeConfig := kcapi.NewConfig()
+	protocol := "https"
+	if !rest.IsConfigTransportTLS(*cfg) {
+		protocol = "http"
+	}
+
+	// cfg.Host is a URL, so we need to parse it so we can properly append the API path
+	baseURL, err := url.Parse(cfg.Host)
+	if err != nil {
+		return nil, fmt.Errorf("unable to interpret config's host value as a URL: %w", err)
+	}
+
+	kubeConfig.Clusters[envtestName] = &kcapi.Cluster{
+		// TODO(directxman12): if client-go ever decides to expose defaultServerUrlFor(config),
+		// we can just use that.  Note that this is not the same as the public DefaultServerURL,
+		// which requires us to pass a bunch of stuff in manually.
+		Server:                   (&url.URL{Scheme: protocol, Host: baseURL.Host, Path: cfg.APIPath}).String(),
+		CertificateAuthorityData: cfg.CAData,
+	}
+	kubeConfig.AuthInfos[envtestName] = &kcapi.AuthInfo{
+		// try to cover all auth strategies that aren't plugins
+		ClientCertificateData: cfg.CertData,
+		ClientKeyData:         cfg.KeyData,
+		Token:                 cfg.BearerToken,
+		Username:              cfg.Username,
+		Password:              cfg.Password,
+	}
+	kcCtx := kcapi.NewContext()
+	kcCtx.Cluster = envtestName
+	kcCtx.AuthInfo = envtestName
+	kubeConfig.Contexts[envtestName] = kcCtx
+	kubeConfig.CurrentContext = envtestName
+
+	contents, err := clientcmd.Write(*kubeConfig)
+	if err != nil {
+		return nil, fmt.Errorf("unable to serialize kubeconfig file: %w", err)
+	}
+	return contents, nil
+}