mockkubeapiserver: Support stringData when creating a secret

This is an edge case in the kube apiserver, but there is special
handling for the stringData field of a secret, that is mapped to
base64 data.

mockkubeapiserver/postresource.go

@@ -18,6 +18,7 @@ package mockkubeapiserver
 
 import (
 	"context"
+	"encoding/base64"
 	"fmt"
 	"io"
 	"net/http"
@@ -73,8 +74,42 @@ func (req *postResource) Run(ctx context.Context, s *MockKubeAPIServer) error {
 		obj.SetGeneration(1)
 	}
 
+	if err := preCreateHook(ctx, obj); err != nil {
+		return err
+	}
+
 	if err := resource.CreateObject(ctx, id, obj); err != nil {
 		return err
 	}
 	return req.writeResponse(obj)
 }
+
+func preCreateHook(ctx context.Context, obj *unstructured.Unstructured) error {
+	gvk := obj.GroupVersionKind()
+	if gvk.Group == "" && gvk.Version == "v1" && gvk.Kind == "Secret" {
+		stringDataAny, found := obj.Object["stringData"]
+		if found {
+			stringDataMap, ok := stringDataAny.(map[string]any)
+			if !ok {
+				return fmt.Errorf("unexpected type for v1.Secret stringData, got %T", stringDataAny)
+			}
+			dataAny, dataFound := obj.Object["data"]
+			if !dataFound {
+				dataAny = make(map[string]any)
+				obj.Object["data"] = dataAny
+			}
+			dataMap, ok := dataAny.(map[string]any)
+			if !ok {
+				return fmt.Errorf("unexpected type for v1.Secret data, got %T", dataAny)
+			}
+			for k, vAny := range stringDataMap {
+				v, ok := vAny.(string)
+				if !ok {
+					return fmt.Errorf("unexpected type for v1.Secret stringData entry, got %T", vAny)
+				}
+				dataMap[k] = base64.StdEncoding.EncodeToString([]byte(v))
+			}
+		}
+	}
+	return nil
+}