code: @GET
    @Path("tokeninfo")
    public Response validate(@QueryParam("access_token") String access_token) {
      checkNotNull(access_token);
  
      DConnection connection = connectionDao.findByAccessToken(access_token);
      LOGGER.debug("Connection {}", connection);
      if (null == connection || hasAccessTokenExpired(connection)) {
        throw new BadRequestRestException("Invalid access_token");
      }
  
      return Response.ok(ImmutableMap.builder()
          .put("user_id", connection.getUserId())
          .put("expires_in", Seconds.secondsBetween(DateTime.now(), new DateTime(connection.getExpireTime())).getSeconds())
          .build())
          .build();
  
    }
docs: Validate an access_token.
  The Oauth2 specification does not specify how this should be done. Do similar to what Google does
  
  @param access_token access token to validate. Be careful about using url safe tokens or use url encoding.
  @return http 200 if success and some basic info about the access_token