Less case sensitive header name (browser compatibility)

[brezniczky]

Hi David!

Thanks a lot for bringing this useful tutorial together (referring to the Medium article)!

In the comments someone mentions - and this is as well my experience in practice with Firefox - that the Authorization header with the credentials reaches the authorizer in all lower case. I also checked with a recent/latest Chromium, it was the same, this commit obviously addresses that.

(And a second note: I am uncertain whether it is a useful suggestion in such illustrative scenarios, but some LICENSE could be useful for this repo as well. I am planning to put a lot of the code to good use for a temporary in-house solution - I pulled a lot of hair out over trying to integrate Cognito for no serious immediate need :) so I guess it can come useful for others too. Of course feel free to ignore this part if you disagree for any reason.)