Don't manually read JSON values, deserialize into a Java object

[IDragonfire]

https://github.com/FAForever/faf-java-api/blob/v0.5.0/src/main/java/com/faforever/api/clan/ClanService.java#L117

@SneakyThrows
  // TODO @dragonfire don't manually read JSON values, deserialize into a Java object?
  public void acceptPlayerInvitationToken(String stringToken, Authentication authentication) {
    Jwt token = jwtService.decodeAndVerify(stringToken);
    JsonNode data = objectMapper.readTree(token.getClaims());

    if (data.get(JwtKeys.EXPIRE_IN).asLong() < System.currentTimeMillis()) {
      throw new ApiException(new Error(ErrorCode.CLAN_ACCEPT_TOKEN_EXPIRE));
    }

    Player player = playerService.getPlayer(authentication);
    Clan clan = clanRepository.findOne(data.get(JwtKeys.CLAN).get(JwtKeys.CLAN_ID).asInt());

    if (clan == null) {
      throw new ApiException(new Error(ErrorCode.CLAN_NOT_EXISTS));
    }

    Player newMember = playerRepository.findOne(data.get(JwtKeys.NEW_MEMBER_ID).asInt());
    if (newMember == null) {
      throw new ProgrammingError("ClanMember does not exist: " + data.get(JwtKeys.NEW_MEMBER_ID).asInt());
    }

    if (player.getId() != newMember.getId()) {
      throw new ApiException(new Error(ErrorCode.CLAN_ACCEPT_WRONG_PLAYER));
    }
    if (newMember.getClan() != null) {
      throw new ApiException(new Error(ErrorCode.CLAN_ACCEPT_PLAYER_IN_A_CLAN));
    }

    ClanMembership membership = new ClanMembership();
    membership.setClan(clan);
    membership.setPlayer(newMember);
    clanMembershipRepository.save(membership);
  }