class Gem::RemoteFetcher

def sign_s3_url(uri, expiration = nil)
  require 'base64'
  require 'openssl'
  unless uri.user && uri.password
    raise FetchError.new("credentials needed in s3 source, like s3://key:secret@bucket-name/", uri.to_s)
  end
  expiration ||= s3_expiration
  canonical_path = "/#{uri.host}#{uri.path}"
  payload = "GET\n\n\n#{expiration}\n#{canonical_path}"
  digest = OpenSSL::HMAC.digest('sha1', uri.password, payload)
  # URI.escape is deprecated, and there isn't yet a replacement that does quite what we want
  signature = Base64.encode64(digest).gsub("\n", '').gsub(/[\+\/=]/) { |c| BASE64_URI_TRANSLATE[c] }
  URI.parse("https://#{uri.host}.s3.amazonaws.com#{uri.path}?AWSAccessKeyId=#{uri.user}&Expires=#{expiration}&Signature=#{signature}")
end