在进行身份验证时，authenticationManager.authenticate报错提示请求体缺失。解决办法是在请求头中设置Content-Type为application/json，并将请求参数以JSON字符串的形式放入请求体中。示例代码如下：

@RestController
@RequestMapping("/api")
public class AuthController {

    @Autowired
    private AuthenticationManager authenticationManager;

    @Autowired
    private JwtTokenUtil jwtTokenUtil;

    @PostMapping("/login")
    public ResponseEntity createAuthenticationToken(@RequestBody LoginRequest loginRequest) throws Exception {

        //身份验证
        try {
            authenticationManager.authenticate(
                    new UsernamePasswordAuthenticationToken(loginRequest.getUsername(), loginRequest.getPassword())
            );
        } catch (Exception e) {
            throw new Exception("用户名或密码错误", e);
        }

        //生成Token
        final UserDetails userDetails = userDetailsService.loadUserByUsername(loginRequest.getUsername());
        final String token = jwtTokenUtil.generateToken(userDetails);

        //返回Token
        return ResponseEntity.ok(new JwtResponse(token));
    }
}

当使用Postman等工具进行测试时，需要在请求头中添加Content-Type为application/json，同时请求体中传入JSON格式的参数，示例如下：

POST http://localhost:8080/api/login

Headers:
Content-Type: application/json

Body:
{
    "username": "admin",
    "password": "admin"
}