Sketch a CertificateSignerV1 shim
Remove password auth stuff--we aren't doing that
Remove credential-related stuff from shim
Sketching shim specs
Rename CertificateSignerV1 to LegacyCertificateSigner
Support blacklisting routes for authentication
Call them authentication exemptions
Partially implement shims
Get signme POST uploads and cert cache working!
Also do coverage on specs

Of course! I found several dead code paths in my specs. Just group coverage as
Source and Specs.
Finish legacy certificate signer shims