解决方法：
重新定义Fegin底层的拦截方式，并将新定义的拦截方式应用到@Fegin注解中。

@Component
public class FeignRequestInterceptor implements RequestInterceptor {
    @Override
    public void apply(RequestTemplate requestTemplate) {
        ServletRequestAttributes attributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
        if (null == attributes) {
            return;
        }
        HttpServletRequest request = attributes.getRequest();
        Enumeration<String> headerNames = request.getHeaderNames();
        if (null == headerNames) {
            return;
        }
        while (headerNames.hasMoreElements()) {
            String name = headerNames.nextElement();
            String values = request.getHeader(name);
            // 跳过 content-length
            if (name.equals("content-length")) {
                continue;
            }
            requestTemplate.header(name, values);
        }
    }
}