I've got many users and the solution i used was many selfoss installations in subfolders.
all is working with apache. but since I'm trying ti use it with nginx, i've got problems.

Selfoss easily working as single installation in a virtualhost
for you : change your root like this :

root /var/www/mydomain.com/selfoss;

(maybe : server_name www.mydomain.com; or server_name rss.mydomain.com; ... can help)
and it should work …

but i never get it working in a subfolder like rss.mydomain.com/user1

if someone could give some help!

thanks

But I keep getting this error message:

2016/03/13 17:05:23 [error] 7909#0: *6 FastCGI sent in stderr: "PHP message: HTTP 404 (GET /mydomain.com/all-v2.14.js)" while reading response header from upstream, client: 179.53.48.73, server: mydomain.com, request: "GET /mydomain.com/all-v2.14.js HTTP/1.1", upstream: "fastcgi://unix:/var/run/php5-fpm.sock:", host: "mydomain.com", referrer: "http://mydomain.com/"

This is m Nginx Server block

server {
listen 80;
#listen [::]:443 ssl;
server_name mydomain.com;
root /var/www/mydomain.com/;
access_log /var/log/nginx/rss.access.log;
error_log /var/log/nginx/rss.error.log;
location ~* \ (gif|jpg|png) {
expires 30d;
}
location ~ ^/favicons/.*$ {
try_files $uri /data/$uri;
}
location ~ ^/thumbnails/.*$ {
try_files $uri /data/$uri;
}
location ~* ^/(data\/logs|data\/sqlite|config\.ini|\.ht) {
deny all;
}
location / {
index index.php index.html index.htm;
try_files $uri /public/$uri /index.php$is_args$args;
}
location ~ \.php$ {
fastcgi_pass unix:/var/run/php5-fpm.sock;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME $document_root/$fastcgi_script_name;
include fastcgi_params;
}
}

Here is a Screen shot of what I get