class Aws::Signers::V3

def sign(http_req)
  date = Time.now.httpdate
  http_req.headers['Date'] = date
  if @credentials.session_token
    http_req.headers['X-Amz-Security-Token'] = @credentials.session_token
  end
  parts = []
  parts << "AWS3-HTTPS AWSAccessKeyId=#{@credentials.access_key_id}"
  parts << "Algorithm=HmacSHA256"
  parts << "Signature=#{signature(date)}"
  http_req.headers['X-Amzn-Authorization'] = parts.join(',')
end

def signature(date)
  sha256_hmac(date)
end