Nginx Whitelist IP, use certificate otherwise - authentication

Question

I am setting up a server for my university which has to be only accessible from inside their network.
This I can easily do with nginx. Unfortunatley there are some people that do not have access to this network/IP range. I could use Basic Authentication With Source IP Whitelisting but I would prefer to use a certificate.
Is there a way to first check, if the access is from within the allowed IP Range and if not asking for a certificate?
I tried something like:
server {
root /var/www/html;
index index.html index.htm index.nginx-debian.html;
listen [::]:443 ssl ipv6only=on; # managed by Certbot
listen 443 ssl; # managed by Certbot
ssl_certificate /etc/letsencrypt/live/test.de/fullchain.pem; # managed by Certbot
ssl_certificate_key /etc/letsencrypt/live/test.de/privkey.pem; # managed by Certbot
include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot
# server_name _;
server_name test.de;
ssl_client_certificate /etc/nginx/client_certs/ca.crt;
ssl_verify_client optional;
error_log /var/log/nginx/errors.log debug;
location / {
satisfy any;
allow 123.0.0.0/16;
allow 456.0.0.0/16;
deny all;
if ($ssl_client_verify != SUCCESS) {
return 403;
}
try_files $uri $uri/ =403;
}
}
server {
if ($host = test.de) {
return 301 https://$host$request_uri;
} # managed by Certbot
listen 80 ;
listen [::]:80 ;
server_name test.de;
return 404; # managed by Certbot
}
which is not working.
I could use a check for the IP before checking the ssl_client_verify like
if ($remote_addr = 1.2.3.4 )
{
proxy_pass http://10.10.10.1;
break;
}
if ($ssl_client_verify != "SUCCESS")
{ return 403; }
but this would not be feasible for every single ip adress.
How could I handle this efficiently?
Thank you in advance
~Fabian

Answer 1

You may be able to use a geo block instead of the allow/deny statements and use $ssl_client_verify as the default value.
For example:
geo $verify {
123.0.0.0/16 "SUCCESS";
456.0.0.0/16 "SUCCESS";
default $ssl_client_verify;
}
server {
if ($verify != "SUCCESS") { return 403; }
...
}
See this document for details.