Java 为什么我的登录终结点不能被任何请求访问

所以，我的朋友的登录页面出现了问题.当她try 向她的API发出请求时，它只会在前端出错，而在API中什么都不会发生.

这是出现在控制台上的错误: CORS策略已阻止从源"http://localhost:3000"访问位于"http://localhost:8082/login"的XMLHttpRequest:对预检请求的响应未通过访问控制判断:请求的资源上不存在"Check-Control-Allow-Origin"标头. Copyright © 2018 - 2019 www.js.com. All rights reserved.粤ICP备16048888号-1

这是登录端点

@Controller
@CrossOrigin(
    origins = "http://localhost:3000",
    allowCredentials = "true"
)
@RequestMapping("/login")
public class AuthenticationController {

@Autowired
AuthenticationManager authenticationManager;

private static final Logger logger = LoggerFactory.getLogger(AuthenticationController.class);

@PostMapping
public ResponseEntity<?> login(
        @RequestBody Login login,
        HttpServletRequest request,
        HttpServletResponse response
){
    logger.debug("Received login request for username: {}", login.getUsername());
    System.out.println("AuthenticationCOntroller");
    SecurityContextRepository securityContextRepository = new HttpSessionSecurityContextRepository();
    UsernamePasswordAuthenticationToken token =
            new UsernamePasswordAuthenticationToken(login.getUsername(), login.getPassword());
    Authentication authentication = authenticationManager.authenticate(token);

    if(authentication.isAuthenticated()){
        User user = (User) authentication.getPrincipal();
        Cookie cookie = CookieUtil.generateCookie(user);
        response.addCookie(cookie);
        return ResponseEntity.ok(authentication.getPrincipal());
    }
}

以下是她的GitHub链接: API个 Front-end

她试图重构她的所有代码，但登录时仍然出错.