Bearer vs. non-bearer (Re: OAUTH SASL and Channel binding)

FWIW, I seethe appeal of bearer tokens.  If you trust the TLS server
PKI then bearer tokens can be implemented with no changes to the
HTTP/TLS stack and *no additional crypto* on the client side.  Heck,
it's even possible to implement bearer token schemes with no
additional crypto anywhere.  This sounds too wonderful too be true,
but it is true, no?

But once you're stuck with a bearer token you're also stuck with
either trusting the TLS server PKI fully, or making changes to the
HTTP/TLS stack.  That seems like an awful bind to me.

So, in principle bearer and signature tokens can both offer reasonable
security (if one adheres to their respective security considerations).
 In practice there are differences, which I hope I captured succinctly
enough above.

I believe the downside of bearer tokens overwhelm the upside -- a
proposition that no doubt requires more discussion.

Nico
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