webminをnginx+SSLでサブディレクトリで動かす

/etc/webmin/config

webprefix=/webmin_subdirectory
webprefixnoredir=0

/etc/webmin/miniserv.conf

port=25252
front_url=https://example.com/webmin_subdirectory/

/etc/nginx/conf.d/ssl.conf

server {
 listen 443;
 root /www/html/;
 server_name example.com;
 client_max_body_size 25M;
 ssl on;
 ssl_certificate     /etc/nginx/cert/server.crt;
 ssl_certificate_key  /etc/nginx/cert/server.key;
 
#Webmin Setting

 location /webmin_subdirectory/ {
 proxy_redirect http://example.com:25252/ https://example.com/webmin_subdirectory/;
 proxy_pass http://127.0.0.1:25252/;
 proxy_read_timeout 3600s;
 proxy_set_header    X-Real-IP  $remote_addr;
 proxy_set_header    X-Forwarded-For $proxy_add_x_forwarded_for;
 proxy_set_header    Host            $host;
 proxy_set_header X-Forwarded-Proto $scheme;
 }
}

nginx、Webminの再起動でhttps://example.com/webmin_subdirectory/でアクセス可能となる。