nginx for https and http always ends up in the http way

This is the first time I try to setup an nginx reverse proxy. What I want is I have a Subversion server running http on port 44801.

Now I want to use nginx to listen on port 80 and forward but also listen on 443, do the ssl termination and then forward.

This is my conf file:

server {
        # Port 80 only on local network
        listen       80;
        server_name  freundx;

        location /svn {
                proxy_set_header Host $host;
                proxy_set_header X-Real-IP $remote_addr;
                proxy_pass   http://freundx:44801/svn;
        }
}


server {
        # ssl is local and external
        listen       443 ssl;
        server_name  freundx some.domain.com;

        ssl_certificate     /etc/niginx/ssl/mycert.crt;
        ssl_certificate_key /etc/niginx/ssl/mycert.key;
        ssl_protocols       TLSv1 TLSv1.1 TLSv1.2;
        ssl_ciphers         HIGH:!aNULL:!MD5;

        location /svn {
                proxy_set_header Host $host;
                proxy_set_header X-Real-IP $remote_addr;
                proxy_pass      http://freundx:44801/svn;
        }
}

For example, when I open https://freundx/svn, following happens:

1. Browser asks (correctly) for the credentials on https
2. Browser asks a second time for credentials, now for http
3. Now I'm on http

Surely there is missing something in the config. But what? ;-)