sub_filter example

location /server1/ {
    proxy_set_header X-Forwarded-Proto $scheme;
    proxy_pass http://127.0.0.1:81/;
    set $domain "test.com";
    sub_filter "//$domain/" "//$host/server1/";
    sub_filter "href=\"/" "href=\"/server1/";
    sub_filter "href='/" "href='/server1/";
    sub_filter "src=\"/" "src=\"/server1/";
    sub_filter "src='/" "src='/server1/";
    sub_filter "url(/" "url(/server1/";
    sub_filter_once off;
    sub_filter_types text/html text/css application/javascript;
}