Rotate/revoke issuer.jwk throws error when origin auto-registers at registry

[haoming29]

Steps to reproduce:

• If you have issuer.jwk under /etc/pelican, and have an origin prefix registered at registry, say /origin1
• rm issuer.jwk
• Run director, registry, and origin
• You would expect the following message:

Error: Namespace /origin1 already registered under a different key

I'm not sure what's the fix for this, which can initiate to some security policy discussions. @bbockelm What's your thoughts on this?

[bbockelm]

That's the expected / desired behavior: if you try to register with a different key, it should be an error (otherwise someone could pretty trivially steal your namespace).

Separately, I would like to have a mechanism to rotate (add / delete) keys that are registered -- for example, if there are multiple origins under a single part of the namespace -- but you still need to have access to the old key to rotate.

[haoming29]

Closed with #561 opened