实现思路：

1：准备一个ThreadLocal变量，供线程之间共享。

2：每个微服务对所有过来的Feign调用进行过滤，然后从请求头中获取User用户信息，并存在ThreadLocal变量中。

3：每个微服务在使用FeignClient调用别的微服务时，先从ThreadLocal里面取出user信息，并放在request的请求头中。

4：封装为一个注解，在启动类上标记即可。

代码样例：

1：ThreadLocal工具类 ：UserInfoContext 

package com.test.domi.common.system;

import com.test.domi.dao.UserInfo;

public class UserInfoContext {
    private static ThreadLocal<UserInfo> userInfo = new ThreadLocal<UserInfo>();
    public static String KEY_USERINFO_IN_HTTP_HEADER = "X-AUTO-FP-USERINFO";

    public UserInfoContext() {
    }

    public static UserInfo getUser(){
        return (UserInfo)userInfo.get();
    }

    public static void setUser(UserInfo user){
        userInfo.set(user);
    }
}

2：准备承载用户信息的userInfo实体类（代码略）

3：编写拦截器 ： TransmitUserInfoFeighClientIntercepter 

package com.test.domi.config;

import com.alibaba.fastjson.JSON;
import com.test.domi.common.system.UserInfoContext;
import com.test.domi.dao.UserInfo;
import feign.RequestInterceptor;
import feign.RequestTemplate;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;

public class TransmitUserInfoFeighClientIntercepter implements RequestInterceptor {

    private static final Logger log = LoggerFactory.getLogger(TransmitUserInfoFeighClientIntercepter.class);
    public TransmitUserInfoFeighClientIntercepter() {
    }

    @Override
    public void apply(RequestTemplate requestTemplate) {
        //从应用上下文中取出user信息，放入Feign的请求头中
        UserInfo user = UserInfoContext.getUser();
        if (user != null) {
            try {
                String userJson = JSON.toJSONString(user);
                requestTemplate.header("KEY_USERINFO_IN_HTTP_HEADER",new String[]{URLDecoder.decode(userJson,"UTF-8")});
            } catch (UnsupportedEncodingException e) {
                log.error("用户信息设置错误",e);
            }
        }
    }
}

4：编写过滤器：TransmitUserInfoFilter 

package com.test.domi.config;

import com.alibaba.fastjson.JSON;
import com.test.domi.common.system.UserInfoContext;
import com.test.domi.dao.UserInfo;
import org.apache.commons.lang.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;

public class TransmitUserInfoFilter implements Filter {

    private static final Logger log = LoggerFactory.getLogger(TransmitUserInfoFeighClientIntercepter.class);
    public TransmitUserInfoFilter() {
    }
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
       this.initUserInfo((HttpServletRequest)request);
       chain.doFilter(request,response);
    }

    private void initUserInfo(HttpServletRequest request){
        String userJson = request.getHeader("KEY_USERINFO_IN_HTTP_HEADER");
        if (StringUtils.isNotBlank(userJson)) {
            try {
                userJson = URLDecoder.decode(userJson,"UTF-8");
                UserInfo userInfo = (UserInfo) JSON.parseObject(userJson,UserInfo.class);
                //将UserInfo放入上下文中
                UserInfoContext.setUser(userInfo);
            } catch (UnsupportedEncodingException e) {
               log.error("init userInfo error",e);
            }
        }
    }

    @Override
    public void destroy() {
    }
}

5：编写注解实现类： EnableUserInfoTransmitterAutoConfiguration 

package com.test.domi.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class EnableUserInfoTransmitterAutoConfiguration {

    public EnableUserInfoTransmitterAutoConfiguration() {
    }

    @Bean
    public TransmitUserInfoFeighClientIntercepter transmitUserInfo2FeighHttpHeader(){
       return new TransmitUserInfoFeighClientIntercepter();
    }

    @Bean
    public TransmitUserInfoFilter transmitUserInfoFromHttpHeader(){
        return new TransmitUserInfoFilter();
    }
}

6：编写注解 EnableUserInfoTransmitter 

package com.test.domi.annotation;

import com.test.domi.config.EnableUserInfoTransmitterAutoConfiguration;
import org.springframework.context.annotation.Import;

import java.lang.annotation.*;

@Documented
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Import({EnableUserInfoTransmitterAutoConfiguration.class})
public @interface EnableUserInfoTransmitter {
}

7：在启动类上标记注解即可使用（无侵入）

package com.test.domi;

import com.test.domi.annotation.EnableUserInfoTransmitter;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;

@EnableDiscoveryClient
@SpringBootApplication
@MapperScan("com.test.domi.dao")
@EnableUserInfoTransmitter
public class TestCommonClient {

    public static void main(String[] args){

        SpringApplication.run(TestCommonClient.class,args);
    }
}