public class OAuth3AuthenticationProcessingFilter{
	public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException,
			ServletException {
		try {
			// 1. 根據用戶請求解析令牌，組裝預登陸對象
			Authentication authentication = tokenExtractor.extract(request);
			if (authentication == null) {
				// 若是預登陸狀態為空，把無狀態登錄清空
				if (stateless && isAuthenticated()) {
					SecurityContextHolder.clearContext();
				}
			}
			else {
				// 2. 根據token 來做真正的認證登錄 Provier
				Authentication authResult = authenticationManager.authenticate(authentication);

				// 3. 登錄成功邏輯
				eventPublisher.publishAuthenticationSuccess(authResult);
				SecurityContextHolder.getContext().setAuthentication(authResult);
			}
		}
		catch (OAuth3Exception failed) {
      // 異常通知邏輯 Spring Event
			...
			return;
		}
		chain.doFilter(request, response);
	}
}

public class BearerTokenExtractor implements TokenExtractor {
	@Override
	public Authentication extract(HttpServletRequest request) {
		// 1. 解析token
		String tokenValue = extractToken(request);
		if (tokenValue != null) {
			// 2. 創建一個authentication 返回
			PreAuthenticatedAuthenticationToken authentication = new PreAuthenticatedAuthenticationToken(tokenValue, "");
			return authentication;
		}
		return null;
	}

	protected String extractToken(HttpServletRequest request) {
		// 1.1 優先從請求header 獲取token
		String token = extractHeaderToken(request);
		// 1.2 若是請求token 中沒有，則獲取請求參數中的 access_token 參數
		if (token == null) {
			token = request.getParameter(OAuth3AccessToken.ACCESS_TOKEN);
		}
		return token;
	}
}