certbot发起web认证请求流程

![](/media/202107/2021-07-17_103854.png)

```mermaid
graph TD;

client_start[客户端发起xxx.com更新请求]-->server_recieve[认证服务器收到请求];
 server_recieve --> server_query_domain[解析域名]
 server_query_domain --> server_query_failed[失败]
 server_query_failed[失败] --> challenge_failed[证书更新失败]
 server_query_domain --> server_query_success[成功]
 server_query_success[成功] --> server_start_challenge[认证服务器发起请求]
 client_start --> client_generate_challenge_file[客户端生成挑战认证文件]
 client_generate_challenge_file --> well-known[http://xxx.com/.well-known/acme-challenge/xxxxxxx]
 server_start_challenge --> server_request_challenge_file[认证服务器通过web访问挑战认证文件]
 server_request_challenge_file -->  server_request_well_known[http://xxx.com/.well-known/acme-challenge/xxxxxxx]
 server_request_well_known --> server_request_challenge_fail[访问失败]
 server_request_challenge_fail --> fail[更新失败]
 server_request_well_known --> server_request_challenge_success[访问成功]
 server_request_challenge_success --> client_generate_certs[客户端生成证书]
 client_generate_certs --> success[更新成功]
 
```