private OAuth20Token fetchTokenFromRegistry(final String accessTokenId) {
        try {
            val token = extractAccessTokenFrom(accessTokenId);
            return getConfigurationContext().getTicketRegistry().getTicket(token, OAuth20Token.class);
        } catch (final InvalidTicketException e) {
            LOGGER.trace(e.getMessage(), e);
            LOGGER.info("Unable to fetch access token [{}]: [{}]", accessTokenId, e.getMessage());
        }
        return null;
    }
Handle post request.

@param request  the request
@param response the response
@return the response entity
@throws Throwable the throwable
support/cas-server-support-oauth-core-api/src/main/java/org/apereo/cas/support/oauth/web/endpoints/OAuth20IntrospectionEndpointController.java