[keycloak-dev] token exchange

[Bill Burke]

On 7/31/17 11:35 AM, Pedro Igor Silva wrote:
> On Fri, Jul 28, 2017 at 5:24 PM, Bill Burke <bburke at redhat.com 
> <mailto:bburke at redhat.com>> wrote:
>
>     I've implemented a simple token exchange API [1] that allows you to
>     exchange an access token created for one client to another
>     client.  The
>     REST API follows the oauth token exchange api [2] very loosely.
>
>     subject_token: a keycloak access token
>
>     audience: takes a client id
>
>     It then converts the access token created for one client and
>     converts it
>     to another.  It lives under the token endpoint.
>
>     The security model is as follows:
>
>     * Authenticate calling client the same way as password grant.
>
>     * The calling client must have service account enabled
>
>     * Service account must have a realm role "token-exchanger" grant
>     edto it
>     or, it must have a client role "token-exchanger" granted to it.  This
>     exchanger client role is a role defined by the target client you are
>     exchanging the token to.
>
>
>     Is this a good security model?  I'm thinking of not creating these
>     roles
>     right now and to enable support for exchange would require
>     defining the
>     roles specified above.
>
>
> I think roles are too coarse-grained to represent this kind of policy. 
> A better option would be to explicitly define the clients that are 
> allowed to exchange tokens for a particular resource server. Eg.:
>
> RS A allows Client B, C and D to exchange their tokens where the 
> target audience is RS A (or if using "resource", a specific resource 
> in RS A).

I changed it a little.  actors are:

* Authenticated client asking for change
* Clients that are the audience of the token being exchanged
* Client you want the token to be exchanged to

So, the authenticated client must be in the audience of the token being 
exchanged, or, have permission to exchange from that particular 
audience.  The authenticated client also must have permission to 
exchange to the audience it wants to exchange to.


>
>
>     Future work would be to have an additional subject_issuer and
>     requested_issuer parameters.  "subject_issuer" would match to a broker
>     alias, so you could exchange a facebook token for a keycloak realm
>     token.  Same thing goes for "requested_issuer". This would allow
>     you to
>     exchange a Keycloak token for a facebook token or some other
>     registered
>     broker.
>
>
> I'm following your discussion in OAuth2 WG. Do we really need these 
> additional paramerters ?
>
> My understanding from the specs is that:
>
> * Facebook -> Keycloak Realm
>   If you pass a "subject_token_type" like 
> "urn:keycloak:params:oauth:token-type:broker-{ALIAS}", where {ALIAS} 
> is the alias of the broker configured to your realm. Assuming {ALIAS} 
> maps to a Facebook broker in your realm, you probably know how to 
> exchange the FB opaque access token to a Keycloak realm token.
>
> * Keycloak -> Facebook
>   If you pass a "requested_token_type" like 
> "urn:keycloak:params:oauth:token-type:broker-{ALIAS}", where 
> {ALIAS} is the alias of the broker configured to your realm. Assuming 
> {ALIAS} maps to a Facebook broker in your realm, you probably know how 
> to exchange the Keycloak token to a FB token.
>
> Or are you thinking about something else ?

I'm conversing with WG to get this new parameter included in the 
specification.  types and issuers shouldn't be mixed IMO. Especially 
when you could standardize oauth to oauth cross-domain exchange pretty 
easily if you had these new parameters where otherwise you'd be 
dependent on the STS's proprietary type definitions.  The spec is way 
too vague for cross-domain exchange.

Bill