feat: add support for URL encoded values

[andrei-cdl]

due to a bug in node.js some clients will end up encoding the value
before base64 which results in the incorrect value being parsed.

ref: nodejs/node#31439

[dougwilson]

Thank you for this pull request. This is unfortunately not how the header works according to the specification. Doing this would have security implications as clients who follow the spec im combination with this change would allow the username as seen by the client be different as seen by the server, by the nature of the colon separator being hidden in the username.

I'm sure the are various clients who can be buggy; I would suggeset filing an issue with the buggy client so they provide a correctly-formatted header.

[andrei-cdl]

ah interesting, thanks for looking into it. I didn't realize there would be security implications due to that change.