    # File lib/ramaze/helper/httpdigest.rb, line 53
          def httpdigest_lookup(username, realm)
            if block_given?
              yield(username)
            elsif respond_to?(:httpdigest_lookup_password)
              httpdigest_lookup_password(username)
            elsif respond_to?(:httpdigest_lookup_plaintext_password)
              plain = httpdigest_lookup_plaintext_password(username)
              Digest::MD5.hexdigest([username, realm, plain].join(':'))
            else
              raise "No password lookup handler found"
            end
          end