class HTTPX::Plugins::DigestAuthentication::Digest

def generate_header(request, response, _iis = false)
  meth = request.verb.to_s.upcase
  www = response.headers["www-authenticate"]
  # discard first token, it's Digest
  auth_info = www[/^(\w+) (.*)/, 2]
  uri = request.path
  params = Hash[auth_info.split(/ *, */)
                         .map { |val| val.split("=") }
                         .map { |k, v| [k, v.delete("\"")] }]
  nonce = params["nonce"]
  nc = next_nonce
  # verify qop
  qop = params["qop"]
  if params["algorithm"] =~ /(.*?)(-sess)?$/
    alg = Regexp.last_match(1)
    algorithm = ::Digest.const_get(alg)
    raise DigestError, "unknown algorithm \"#{alg}\"" unless algorithm
    sess = Regexp.last_match(2)
    params.delete("algorithm")
  else
    algorithm = ::Digest::MD5
  end
  if qop || sess
    cnonce = make_cnonce
    nc = format("%<nonce>08x", nonce: nc)
  end
  a1 = if sess
    [algorithm.hexdigest("#{@user}:#{params["realm"]}:#{@password}"),
     nonce,
     cnonce].join ":"
  else
    "#{@user}:#{params["realm"]}:#{@password}"
  end
  ha1 = algorithm.hexdigest(a1)
  ha2 = algorithm.hexdigest("#{meth}:#{uri}")
  request_digest = [ha1, nonce]
  request_digest.push(nc, cnonce, qop) if qop
  request_digest << ha2
  request_digest = request_digest.join(":")
  header = [
    %(username="#{@user}"),
    %(nonce="#{nonce}"),
    %(uri="#{uri}"),
    %(response="#{algorithm.hexdigest(request_digest)}"),
  ]
  header << %(realm="#{params["realm"]}") if params.key?("realm")
  header << %(algorithm=#{params["algorithm"]}") if params.key?("algorithm")
  header << %(opaque="#{params["opaque"]}") if params.key?("opaque")
  header << %(cnonce="#{cnonce}") if cnonce
  header << %(nc=#{nc})
  header << %(qop=#{qop}) if qop
  header.join ", "
end

def initialize(user, password)
  @user = user
  @password = password
  @nonce = 0
end

def make_cnonce
  ::Digest::MD5.hexdigest [
    Time.now.to_i,
    Process.pid,
    SecureRandom.random_number(2**32),
  ].join ":"
end

def next_nonce
  @nonce += 1
end