Hey Peter -

I haven't read all of your comments yet, but I wanted to clarify one point
about client impersonation and installed apps.  The cuirrent text is
unrealistic, but your request would push it the wrong way.  CC'ing Torsten
as well.

---------------------
OLD:
  The authorization server SHOULD issue access tokens with limited
  scope and duration to clients incapable of authenticating.

NEW:
  If the authorization server issues access tokens to clients
  that are incapable of authenticating, the scope and duration of
  such tokens SHOULD be limited.

RATIONALE: We're not actively RECOMMENDING authorization servers are to
issue such tokens, are we?
---------------------

We are most definitely recommending that clients that have no way of
authenticating are issued long-lived credentials to access user data.

Most installed applications work as follows:
- they ask the user for their password
- they save the password to disk

That's a horrible security problem, because it means you cannot upgrade user
authentication to anything stronger than a password.  Client certificates,
one time passwords, risk based authentication, throw it all out the window.
 If you're going to let installed apps authenticate with just a password,
nothing else you do to improve authentication is going to help.

This is a blocking issue for rolling out stronger forms of user
authentication, and it's one of the main reasons I care about OAuth2.

Think IMAP and XMPP clients running on Windows desktops.  They are
important, and we need a way to migrate them off of saving passwords.

So the current text basically says that you should issue temporary
credentials to native apps.  That's not practical.  Native apps end up
needing permanent or near-permanent credentials.  Expirations need to be
measured in months.  And the credentials are going to be issued to stock
IMAP and XMPP clients that don't have any way of authenticating themselves.

The advantage with OAuth2 over passwords is that
a) the refresh tokens are unguessable.
b) the refresh tokens aren't sent directly to the IMAP and XMPP servers,
they are restricted to authorization servers.
c) if you've got a managed machine (think Kerberos logins), you can create
flows that bridge from those managed credentials to temporary access
credentials.

Cheers,
Brian
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