Improve types and type checks

[peternedap]

Description of changes:

• AuthenticatorParams type is now exported, making it easier to typecheck params before passing them to the handle function
• The return type of the handle function has been narrowed to exclude undefined and null.
• Pino dependency has been updated to a typed release
• Type casts have been made explicit
• Strict type checking has been enabled in the source files and explicitly disabled in the test files

[nanderv]

Nice :). This would make code I'm working on cleaner.

[jeandek]

Hi Peter,
Thanks for your contribution. We're looking to release a new version of the package this week, so I will try to review this ASAP.
Cheers,
Jean

[jeandek]

I had to rebase on top of the latest changes, but otherwise this looks good to me.