# File lib/www/mechanize/chain/auth_headers.rb, line 38
        def gen_auth_header(uri, request, auth_header, is_IIS = false)
          @@nonce_count += 1
  
          auth_header =~ /^(\w+) (.*)/
  
          params = {}
          $2.gsub(/(\w+)=("[^"]*"|[^,]*)/) {
            params[$1] = $2.gsub(/^"/, '').gsub(/"$/, '')
          }
  
          a_1 = "#{@user}:#{params['realm']}:#{@password}"
          a_2 = "#{request.method}:#{uri.path}"
          request_digest = ''
          request_digest << Digest::MD5.hexdigest(a_1)
          request_digest << ':' << params['nonce']
          request_digest << ':' << ('%08x' % @@nonce_count)
          request_digest << ':' << CNONCE
          request_digest << ':' << params['qop']
          request_digest << ':' << Digest::MD5.hexdigest(a_2)
  
          header = ''
          header << "Digest username=\"#{@user}\", "
          if is_IIS then
            header << "qop=\"#{params['qop']}\", "
          else
            header << "qop=#{params['qop']}, "
          end
          header << "uri=\"#{uri.path}\", "
          header << %w{ algorithm opaque nonce realm }.map { |field|
            next unless params[field]
            "#{field}=\"#{params[field]}\""
          }.compact.join(', ')

          header << "nc=#{'%08x' % @@nonce_count}, "
          header << "cnonce=\"#{CNONCE}\", "
          header << "response=\"#{Digest::MD5.hexdigest(request_digest)}\""
  
          return header
        end