UCAN specification

[Alan Karp]

https://ucan-staging.pages.dev/specification/

I read through it this afternoon (skipping the policy language and crypto heavy sections).  I have some quibbles about the presentation, but the design looks solid from a capability perspective.  

The main thing I think is unnecessary is using DIDs.  They probably went that way because they use long-lived keys instead of a different key pair per certificate.

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Alan Karp