fix: don't use docker config cache if it's empty

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test: add unit test

fix comments

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revert test change

fix comments

pkg/credentialprovider/provider.go

@@ -58,6 +58,10 @@ type CachingDockerConfigProvider struct {
 	Provider DockerConfigProvider
 	Lifetime time.Duration
 
+	// ShouldCache is an optional function that returns true if the specific config should be cached.
+	// If nil, all configs are treated as cacheable.
+	ShouldCache func(DockerConfig) bool
+
 	// cache fields
 	cacheDockerConfig DockerConfig
 	expiration        time.Time
@@ -96,7 +100,10 @@ func (d *CachingDockerConfigProvider) Provide(image string) DockerConfig {
 	}
 
 	klog.V(2).Infof("Refreshing cache for provider: %v", reflect.TypeOf(d.Provider).String())
-	d.cacheDockerConfig = d.Provider.Provide(image)
-	d.expiration = time.Now().Add(d.Lifetime)
-	return d.cacheDockerConfig
+	config := d.Provider.Provide(image)
+	if d.ShouldCache == nil || d.ShouldCache(config) {
+		d.cacheDockerConfig = config
+		d.expiration = time.Now().Add(d.Lifetime)
+	}
+	return config
 }