WEBrick::HTTPAuth::DigestAuth authentication is vulnerable to regular expression denial of service (ReDoS)

The private instance method `split_param_value` in class `WEBrick::HTTPAuth::DigestAuth` uses a regular expression that is vulnerable to denial of service due to catastrophic backtracking.

#!/usr/bin/env ruby

require 'webrick'

config = { :Realm => 'DigestAuth example realm' }

htdigest = WEBrick::HTTPAuth::Htdigest.new 'my_password_file'
htdigest.set_passwd config[:Realm], 'username', 'password'
htdigest.flush

config[:UserDB] = htdigest

digest_auth = …