Add support for Bindle client authn

[vdice]

Wagi recently updated its Bindle dependency in #152. The updated Bindle client takes an authn token, which in #152 we just set to NoAuth/anonymous auth.

Bindle currently supports http/basic auth (username and password) and OIDC.

I propose we start with the former and wait to see if demand for OIDC support arises.

For http/basic, I believe we just need to add a way for wagi to consume username and password values and then invoke the implementations already existing in Bindle.