NGINX Extract DN from pem cert

gistfile1.txt

map  $ssl_client_s_dn  $ssl_client_s_dn_cn {
        default           "";
        ~CN=(?<CN>[^\/,]+) $CN;
}

map  $ssl_client_s_dn  $ssl_client_s_dn_o {
        default           "";
        ~O=(?<O>[^\/,]+) $O;
}

Exmaple:
server {
        listen 443;
        server_name localhost;
        ssl on;
        ssl_certificate /root/ssl/private/nginx-selfsigned.crt;
        ssl_certificate_key /root/ssl/private/nginx-selfsigned.key;
        ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
        #setting for mutual ssl with client
        ssl_client_certificate /root/ssl/private/client.crt;
        ssl_verify_client optional_no_ca;
        ssl_verify_depth 2;

        location / {
                default_type text/plain;
                if ($request_uri ~* "(?:\/)(?<realm_id>([^\/]+))(?:\/*.*)" ) {
                        set $realm_id $1;
                }

                if ($realm_id != $ssl_client_s_dn_o) {
                        return 401 "Provided cert can't access $realm_id";
                }
        }

        location ~* (?:\/)(?<realm_id>([^\/]+))(?:\/*.*) {
                default_type text/plain;
                if ($realm_id != $ssl_client_s_dn_o) {
                        return 401 "Provided cert can't access $realm_id";
                }                
        }

        location = /cn {
                return 200 $ssl_client_s_dn_cn;
                # return 200 "nothing";
                default_type text/plain;
        }

        location = /o {
                return 200 $ssl_client_s_dn_o;
                # return 200 "nothing";
                default_type text/plain;
        }
}