loadAuthentication.java

    @Override
	public OAuth2Authentication loadAuthentication(String accessToken) throws AuthenticationException, InvalidTokenException {

		MultiValueMap<String, String> formData = new LinkedMultiValueMap<String, String>();
		formData.add(tokenName, accessToken);
		HttpHeaders headers = new HttpHeaders();
		headers.set("Authorization", getAuthorizationHeader(clientId, clientSecret));
		Map<String, Object> map = postForMap(checkTokenEndpointUrl, formData, headers);

		if (map.containsKey("error")) {
			logger.debug("check_token returned error: " + map.get("error"));
			throw new InvalidTokenException(accessToken);
		}

		Assert.state(map.containsKey("client_id"), "Client id must be present in response from auth server");
		return tokenConverter.extractAuthentication(map);
	}