Add :private config option

Use presigned_url if S3 objects are private.

config/amazon_s3.example.yml

@@ -19,6 +19,9 @@ production:
   # Folder where attachment thumbnails are stored
   # thumbnails_folder: thumbnails/
 
+  # Whether objects are private, needing presigned URLs (default false)
+  # private: true
+
 development:
   # Copy configuration from `production` if desired
 

lib/amazon_s3/configuration.rb

@@ -23,6 +23,7 @@ def initialize
         :region             => nil,
         :attachments_folder => nil,
         :thumbnails_folder  => nil,
+        :private            => false,
       }
     end
 
@@ -66,6 +67,10 @@ def region
       @config[:region]
     end
 
+    def private?
+      @config[:private]
+    end
+
     def attachments_folder
       str = @config[:attachments_folder]
       if str.present?

lib/amazon_s3/connection.rb

@@ -46,7 +46,11 @@ def delete(filename, target_folder = @@config.attachments_folder)
 
       def object_url(filename, target_folder = @@config.attachments_folder)
         object = self.object(filename, target_folder)
-        object.public_url
+        if @@config.private?
+          object.presigned_url(:get)
+        else
+          object.public_url
+        end
       end
 
       def get(filename, target_folder = @@config.attachments_folder)