gistfile1.rb

require 'digest/md5'

# A little HTTP Digest authentication calculator, based on the C code in RFC2617
class DigestAuthCalc < Struct.new(:algorithm, :username, :realm, :password, :nonce,
                                  :cnonce, :nc, :qop, :method, :uri, :entity)

  # Calculates the "response" header parameter from the data in the struct
  def response
    hash_sequence(ha1, nonce) do |resp|
      resp << [nc, cnonce, qop] if qop
      resp << hash_sequence(method, uri) do |ha2|
        ha2 << entity_hash if qop && qop =~ /^auth-int/i
      end
    end
  end

  private
  def entity_hash
    md5hash(entity)
  end

  def ha1
    _ha1 = md5hash(username, realm, password)
    if algorithm =~ /^md5-sess/i
      md5hash(_ha1, nonce, cnonce)
    else
      _ha1
    end
  end

  def hash_sequence(*args)
    yield args
    md5hash(args)
  end

  def md5hash(*args)
    Digest::MD5.hexdigest(args.flatten.compact.join(":"))
  end
end