OAuth2ClientContextFilter

處理UserRedirectRequiredException異常，做瀏覽器跳轉。當用戶跳轉到本地login時，如果發現UserRedirectRequiredException異常，跳轉認證中心 oauth/authorize介面，傳引數response_type，client_id，redirect_uri，scope。 （很熟悉吧）

認證中心發現未登入轉到登陸頁面。 登陸完之後會跳轉redirect_uri對應頁面（客戶端登入APi），這個請求帶code引數的，

然後走過濾器鏈，發現OAuth2ClientAuthenticationProcessingFilter認證通過了。 轉向快取的請求（

OAuth2ClientAuthenticationProcessingFilter

繼承AbstractAuthenticationProcessingFilter實現attemptAuthentication方法。和UsernamePasswordFilter是一類。

	//在OAuth2ClientAuthenticationProcessingFilter中
     @Override
	public Authentication attemptAuthentication(HttpServletRequest request, HttpServletResponse response)
			throws AuthenticationException, IOException, ServletException {

		OAuth2AccessToken accessToken;
		try {
			accessToken = restTemplate.getAccessToken();
		} catch (OAuth2Exception e) {
			BadCredentialsException bad = new BadCredentialsException("Could not obtain access token", e);
			publish(new OAuth2AuthenticationFailureEvent(bad));
			throw bad;			
		}
		try {
			OAuth2Authentication result = tokenServices.loadAuthentication(accessToken.getValue());
			if (authenticationDetailsSource!=null) {
				request.setAttribute(OAuth2AuthenticationDetails.ACCESS_TOKEN_VALUE, accessToken.getValue());
				request.setAttribute(OAuth2AuthenticationDetails.ACCESS_TOKEN_TYPE, accessToken.getTokenType());
				result.setDetails(authenticationDetailsSource.buildDetails(request));
			}
			publish(new AuthenticationSuccessEvent(result));
			return result;
		}
		catch (InvalidTokenException e) {
			BadCredentialsException bad = new BadCredentialsException("Could not obtain user details from token", e);
			publish(new OAuth2AuthenticationFailureEvent(bad));
			throw bad;			
		}

	}
 

accessToken = restTemplate.getAccessToken(); 訪問認證伺服器獲取token的方法。 如果發現沒有code丟擲UserRedirectRequiredException異常。 如果獲取成功，那就離登入成功不遠了。

	   //在AuthorizationCodeAccessTokenProvider中
      public String obtainAuthorizationCode(OAuth2ProtectedResourceDetails details, AccessTokenRequest request)
			throws UserRedirectRequiredException, UserApprovalRequiredException, AccessDeniedException,
			OAuth2AccessDeniedException {

		AuthorizationCodeResourceDetails resource = (AuthorizationCodeResourceDetails) details;

		HttpHeaders headers = getHeadersForAuthorizationRequest(request);
		MultiValueMap<String, String> form = new LinkedMultiValueMap<String, String>();
		if (request.containsKey(OAuth2Utils.USER_OAUTH_APPROVAL)) {
			form.set(OAuth2Utils.USER_OAUTH_APPROVAL, request.getFirst(OAuth2Utils.USER_OAUTH_APPROVAL));
			for (String scope : details.getScope()) {
				form.set(scopePrefix + scope, request.getFirst(OAuth2Utils.USER_OAUTH_APPROVAL));
			}
		}
		else {
			form.putAll(getParametersForAuthorizeRequest(resource, request));
		}
		authorizationRequestEnhancer.enhance(request, resource, form, headers);
		final AccessTokenRequest copy = request;

		final ResponseExtractor<ResponseEntity<Void>> delegate = getAuthorizationResponseExtractor();
		ResponseExtractor<ResponseEntity<Void>> extractor = new ResponseExtractor<ResponseEntity<Void>>() {
			@Override
			public ResponseEntity<Void> extractData(ClientHttpResponse response) throws IOException {
				if (response.getHeaders().containsKey("Set-Cookie")) {
					copy.setCookie(response.getHeaders().getFirst("Set-Cookie"));
				}
				return delegate.extractData(response);
			}
		};
		// Instead of using restTemplate.exchange we use an explicit response extractor here so it can be overridden by
		// subclasses
		ResponseEntity<Void> response = getRestTemplate().execute(resource.getUserAuthorizationUri(), HttpMethod.POST,
				getRequestCallback(resource, form, headers), extractor, form.toSingleValueMap());

		if (response.getStatusCode() == HttpStatus.OK) {
			// Need to re-submit with approval...
			throw getUserApprovalSignal(resource, request);
		}

		URI location = response.getHeaders().getLocation();
		String query = location.getQuery();
		Map<String, String> map = OAuth2Utils.extractMap(query);
		if (map.containsKey("state")) {
			request.setStateKey(map.get("state"));
			if (request.getPreservedState() == null) {
				String redirectUri = resource.getRedirectUri(request);
				if (redirectUri != null) {
					request.setPreservedState(redirectUri);
				}
				else {
					request.setPreservedState(new Object());
				}
			}
		}

		String code = map.get("code");
		if (code == null) {
			throw new UserRedirectRequiredException(location.toString(), form.toSingleValueMap());
		}
		request.set("code", code);
		return code;

	}