Regex to extract username from header value

[jjhuff]

I use this to handle auth from Google application proxy. Unfortunately, the header value looks like:
accounts.google.com:justin@example.com
It works fine, but it's a bit verbose.

It'd be awesome if I could specify a regex to just extract part of the value as the username like
accounts.google.com:(.*) or accounts.google.com:(.*)@example.com

Otherwise, it's working great. Thanks!

[cwaldbieser]

I pushed branch "user_transform" and added an example in the README. Basically, you should be able to define a callable that accepts the value from the header and return the actual value you want passed to JupyterHub. You can use a regex or any other string manipulation or mapping you want.

I think you have to use staticmethod on any function you try to assign.

I haven't tested this. Let me know if it works, and I'll merge it into the main line.