I have no idea how I managed to do this but I ended up in a caching loop. I went to /wp-login.php or /wp-admin/ tried logging in but was always redirected to the login page with a "reauth=1″ appended to the login URL.
I manually deleted the folder containing my fastcgi_cache and was able to proceed.
#move next 3 lines to /etc/nginx/nginx.conf if you want to use fastcgi_cache across many sites fastcgi_cache_path /var/cache/nginx levels=1:2 keys_zone=WORDPRESS:500m inactive=60m; fastcgi_cache_key "$scheme$request_method$host$request_uri"; fastcgi_cache_use_stale error timeout invalid_header http_500; fastcgi_ignore_headers Cache-Control Expires Set-Cookie;
Would you mind having a look at my vhost file: http://pastebin.com/20nxEcij
I’ve left it complete to make sure you get the full picture, if you want, I can cut out everything except the caching stuff for easier readability?