Add BearerToken with allowlist example

[emcfarlane]

Creates a new example based on bearer tokens, a common authentication requirement, with a new helper method BearerToken to assist. This is used to provide the example. A new method Echo is added to the example ping service to showcase conditionally applying authentication based on the Procedure name.

Resolves #11

[Galaf]

Is it possible to prioritize this to add Bearer Token support?

Do you need anything to finish this PR and then proceed with release? I'm happy to help if need be :)