class AWS::S3::PresignedPost

def refine(opts)
  self.class.new(bucket, {
                   :conditions => conditions,
                   :key => key,
                   :metadata => metadata,
                   :secure => secure?,
                   :content_length => content_length,
                   :expires => expires,
                   :ignore => ignored_fields
                 }.merge(@fields).
                 merge(opts))
end