@claus I had to make one mod to get your rewrite to work properly, change the http to https.
location ~ /\+\+api\+\+($|/.*) {
rewrite ^/(\+\+api\+\+\/?)+($|/.*) /VirtualHostBase/https/$server_name/mysite/++api++/VirtualHostRoot/$2 break;
proxy_pass http://backend;
}