Access header information from error callback

[cbargren]

It would be nice if there was a way to access the header information for a failure in the error callback. This is helpful for checking the scope of the token that was used to make a request so you can inform the user if they need new permissions. I have a way to do that here, but the fix is a little janky and there might be a better long-term solution. I can fix this up and PR it if you would like, though.

[kaizensoze]

Sure, I'll add it now.