[Nix-dev] PoC: keys in XML files

[Игорь Пашев]

Most of Java apps use XML file to store configuration.
The idea is to keep this interface instead of multiple yet
limited number of options, complete set of which you may never know.
Especially with plugins ;-)

So if an app wants XML, it gets it. But since they may include secrets,
we need to deal with that. And the answer is XInclude.

Some apps may support XInclude, others need runtime support (xmllint
--xinclude ...). Anyway, we just write XML files, and extract keys, if
any, at nix evaluation time.

See example for Jenkins:
https://github.com/zalora/nixsap/commit/83e08fdb873016154c2880265b6e08ec653af644
(extracting keys)
https://github.com/zalora/nixsap/commit/1a4d734a4110a05e08b88b539b7ea4939d2d1c36
(Jenkins app)