@@ -12,6 +12,29 @@ Set this buildpack on an exiting app:
1212
1313 $ heroku buildpacks:set https://github.com/mfine/heroku-buildpack-stack
1414
15+### Templating stack.yaml
16+
17+To avoid committing secrets into `stack.yaml` for access to private
18+repos, an app's config vars values can be substituted for tags
19+enclosed in double brackets. For example, given a `stack.yaml` containing:
20+
21+ packages:
22+ -location:
23+ git: https://mfine:{{GITPASS}}@github.com/mfine/heroku-buildpack-stack.git
24+
25+and an application with config vars:
26+
27+ $ heroku config -app calm-storm-51595
28+ === murmuring-beyond-51595 Config Vars
29+ GITPASS: abc123
30+ $
31+
32+before compilation, the `stack.yaml` will be substituted as follows:
33+
34+ packages:
35+ -location:
36+ git: https://mfine:abc123@github.com/mfine/heroku-buildpack-stack.git
37+
1538[1]: https://github.com/mfine/heroku-buildpack-stack
1639[2]: http://devcenter.heroku.com/articles/buildpacks
1740[3]: https://github.com/commercialhaskell/stack