Tente isto:
server {
server_name svn.domain.com;
listen 443 ssl;
root /var/www/html;
error_log /var/log/nginx/svn.error.log;
location / {
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_pass http://10.0.1.90/svn/;
}
}