Re: [sipcore] I-D Action: draft-ietf-sipcore-sip-token-authnz-02.txt

[Paul Kyzivat <[e-mail]>]

On 7/11/19 10:07 AM, Christer Holmberg wrote:
> Hi,
> 
>      >>>> All I am saying is that one should not send a token to someone that it has NOT been issued for.
>      >>>
>      >>>     Then you are saying that a token should *never* be included in a request
>      >>>     to a target for which you have not received a challenge some time in the
>      >>>     past.
>      >>>
>      >>>     That is a bit extreme, but I guess you can specify that if you think it
>      >>>     is the right thing to do.
>      >>
>      >> That is my understanding of the generic OAuth security considerations: you don't give a token to someone it was not intended for.
>      >>
>      >> Of course, if you know (based on whatever configuration/policy) that it's ok to give the token to the target I guess you could do it.
>      >>
>      >>>     But note that this logic won't always work for Proxy-Authenticate. You
>      >>>     *might* know that a particular proxy will be visited (if it is mentioned
>      >>>     on a Route header), but it is pretty common for the request to visit
>      >>>     proxies unknown (at least in advance) to the UAC.
>      >>
>      >> It is important to remember that, since the token needs to be protected, a proxy needs to have the
>      >> associated protection credentials to be able to access the token.
>      >
>      > I'm lost here. How is the token protected? Is it because it is passed by
>      > reference, and other credentials are needed to dereference it? Or is it
>      > passed by value but encrypted?
> 
>      That depends on how your protect it.
> 
>      If the oauth2 token itself is encrypted, and only authorized entities can decrypt it, then I guess it does not matter if a non-authorized user gets it, as it will not be able to use it.

Is this going to be defined, or is the intent to leave it open?
I don't understand how things can work if it is left open.

>      But, if the oauth2 token is sent in "plain text", then the SIP signaling needs to be protected/encrypted. But, in that case, if I make a phone call to you, and the call itself is valid, then I should not send you the oauth2 token unless it's meant for you, because once you decrypt the signaling you will have access to it.
> 
>     What is important is that a non-authorized user should not have access to a non-protected oauth2 token.

I don't see how this can work. How does the UAC *know* if the server it 
is sending credentials to is authorized to receive those credentials?

In general the UAC doesn't know what proxies and UAS the request will 
visit. All it knows is the request-URI. Since there generally isn't a 
direct connection from UAC to UAS TLS authentication doesn't help.

	Thanks,
	Paul