SPKI Certificates
Rather than binding a public key to an identity, what is really wanted is to bind a public key to an action or authorization. This is the goal of SPKI (simple public key infrastructure).
http://www.clark.net/pub/cme/spki-reqts.html
http://www.clark.net/pub/cme/html/spki.txt
http://theory.lcs.mit.edu/~rivest/publications.html