change image library and refactor thumbnails service

thumbnails/pkg/thumbnail/imgsource/imgsource.go

@@ -16,15 +16,16 @@ type Source interface {
 	Get(ctx context.Context, path string) (image.Image, error)
 }
 
-// WithAuthorization puts the authorization in the context.
-func WithAuthorization(parent context.Context, authorization string) context.Context {
+// ContextSetAuthorization puts the authorization in the context.
+func ContextSetAuthorization(parent context.Context, authorization string) context.Context {
 	return context.WithValue(parent, auth, authorization)
 }
 
-func authorization(ctx context.Context) string {
+// ContextGetAuthorization gets the authorization from the context.
+func ContextGetAuthorization(ctx context.Context) (string, bool) {
 	val := ctx.Value(auth)
 	if val == nil {
-		return ""
+		return "", false
 	}
-	return val.(string)
+	return val.(string), true
 }