Infer app repo from the referer header

[zpnk]

This would make it even easier to drop a deploy button in a GitHub readme.

[gjreasoner]

Not sure if the intention is to solely rely the referrer or not but there are some cases where it might not work that would need to be considered, such as if someone were to copy the link and slack it to someone else. Or depending on the browser conditions/users privacy concerns, a lot of times a referrer can be unset easily.

[zpnk]

Hey @gjrdiesel! 👋 Thanks for the feedback! You're right, this would only work on requests coming directly from GitHub, and even then only in certain cases.

We'd definitely want to keep our current support for specifying the repo explicitly via the ?repo= query param.

This primarily would be a small quality of life improvement that could mesh nicely with our eventual support for branch deploys (#6). IE, if the repo is inferred from the referer, the maintainer doesn't have to change the button link in the readme to deploy different branches.

This isn't high priority by any means, but it is something Heroku supports for example, so it could be nice to have even for the small set of use cases.