class AWS::S3::Request

def add_authorization! credentials
  if token = credentials.session_token
    headers["x-amz-security-token"] = token
  end
  secret = credentials.secret_access_key
  signature = Core::Signer.sign(secret, string_to_sign, 'sha1')
  signature = URI.escape(signature)
  headers["authorization"] = "AWS #{credentials.access_key_id}:#{signature}"
end