let's encrypt 生成证书时，404 not found的错误

今天在服务器上为另一个域名添加ssl，结果出现了http://xxx/.well-known/… 404 not found的错误
[root@fungli myxhs]# sudo certbot certonly --webroot -w /webser/www/myxhs -d xxx.xxx.cn -m [email protected] --agree-tos
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator webroot, Installer None
Starting new HTTPS connection (1): acme-v01.api.letsencrypt.org
Obtaining a new certificate
Performing the following challenges:
http-01 challenge for xxx.xxx.cn
Using the webroot path /webser/www/myxhs for all unmatched domains.
Waiting for verification...
Cleaning up challenges
Failed authorization procedure. xxx.xxx.cn (http-01): urn:acme:error:unauthorized :: The client lacks sufficient authorization :: Invalid response from http://xxx.xxx.cn/.well-known/acme-challenge/5vo0TVEuIagsjJ5Z3o0s9Kpvbi2I4Mz21hyg3SB3y2c: "


404 Not Found
"

IMPORTANT NOTES:
 - The following errors were reported by the server:

   Domain: xxx.xxx.cn
   Type:   unauthorized
   Detail: Invalid response from
   http://xxx.xxx.cn/.well-known/acme-challenge/5vo0TVEuIagsjJ5Z3o0s9Kpvbi2I4Mz21hyg3SB3y2c:
   "
   
   
   
404 Not Found
   
"

   To fix these errors, please make sure that your domain name was
   entered correctly and the DNS A/AAAA record(s) for that domain
   contain(s) the right IP address.

后发现是nginx配置的错误，我的项目是基于Laravel5开发的，需要在nginx配置中加上一段：
#myxhs 是我项目的根目录，而站点的解析目录需要指定到/var/www/html/myxhs/public下。
location ~ /.well-known {
    root /var/www/html/myxhs;
    allow all;
}

.well-known是什么文件夹？
.well-known 文件夹是申请SSL时自动生成的，删除不影响SSL工作，但是当SSL过期续期后会再次自动生成