sign (OpenID::Association)

    # File lib/openid/association.rb, line 96
        def sign(pairs)
          kv = Util.seq_to_kv(pairs)
          case assoc_type
          when 'HMAC-SHA1'
            CryptUtil.hmac_sha1(@secret, kv)
          when 'HMAC-SHA256'
            CryptUtil.hmac_sha256(@secret, kv)
          else
            raise ProtocolError, "Association has unknown type: "\
              "#{assoc_type.inspect}"
          end
        end