This morning I noticed I haven’t upgraded WordPress MU Domain Mapping plugin to the latest version. It supposedly brings better SSL support. And after upgrading I couldn’t log in to my mapped domain blogs (e.g. this blog). Wasn’t it a great way to start my morning?

After some digging, I found out the problem was because I don’t have one PHP(?) parameter – HTTPS – passed properly. It should set to True whenever one is using SSL connection otherwise there’s no way the PHP process can know if the connection is secure or not. Previous version of WPMUDM have a bug in which skips SSL check but in turn enables using HTTPS even without such parameter. Decided it’s my fault (I believe it would completely breaks phpMyAdmin), adding the parameter then I did.

But it’s not that simple: I’m using unified config for both my SSL and non-SSL connection’s PHP include. Splitting the config would make the duplication worse (it’s already relatively bad as it is) so that’s not an option. Using the evil if is also not a solution since it doesn’t support setting fastcgi_param inside it.

Then the solution hit me. The map module – a module specifically made for things like this and to avoid usage of if. I tested it and indeed worked as expected.

Here be the config:

...
http {
  ...
  map $scheme $fastcgi_https {
    https 1;
    default 0;
  }
  ...
  server {
    ...
    location ~ .php$ {
      ...
      fastcgi_param HTTPS $fastcgi_https;
    }
...

And WordPress MU Domain Mapping is now happy.

Update 2012-02-20: nginx version 1.1.11 and up now have $https variable. No need to have that map anymore.