[keycloak-dev] token exchange
Bill Burke
bburke at redhat.com
Mon Aug 14 09:42:07 EDT 2017
CLI tool I wrote doesn't allow token exchange, yet, but you're correct,
I'm thinking of using it to perform token exchange.
Our ID tokens are not signed right now. Also you still need client to
client exchange so that you can "downgrade" a token to talk to an
untrusted service. I've also added new fine-grain permissions
"exchange-from" and "exchange-to".
For example, lets say Client A gets token and invokes on service B which
needs to invoke on untrusted service C.
1. Service B asks to exchange the token created for A to talk to C
2. Token exchange endpoint looks at issuer, its A, so it sees if service
B has permission to "exchange-from" tokens created for A
3. Token exchange then sees if B has permission to "exchange-to" B.
FYI, I'm also expanding this so that you can exchange an access token
for a social provider token. Automatic refreshes and everything if the
provider supports it. Gonna change how client initiated linking works
too so that instead of doing the silly hash algorithm required by the
call, clients would call the exchange first, get an error response like
"not linked" that contained a browser URL that the client can use to
create the link.
Also no reason I couldn't do the same for exchange an external token to
a internal one. Would work the same as our IDP, import the user, etc.
On 8/14/17 7:06 AM, Stian Thorgersen wrote:
> I'm assuming the basic token exchange service comes from the way the
> CLI tool works? I.e. you login to the tool then it allows exchanging
> the token for a particular CLI client?
>
> Would it not be better to obtain an ID token and use direct grant to
> obtain a token for the client using the ID token as the authentication
> mechanism?
>
> On 1 August 2017 at 19:10, Pedro Igor Silva <psilva at redhat.com
> <mailto:psilva at redhat.com>> wrote:
>
> On Mon, Jul 31, 2017 at 1:54 PM, Bill Burke <bburke at redhat.com
> <mailto:bburke at redhat.com>> wrote:
>
> >
> >
> > On 7/31/17 12:18 PM, Bill Burke wrote:
> >
> >
> >
> > 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.
> >
> > Good idea to change it to use the fine grain admin permissions.
> There's a
> > couple of issues/problems with doing this that I think are
> easily done:
> >
> > * public clients can't have service accounts.
> > * Client Policy looks at kc_client_id attribute which is pulled
> from the
> > issuedFor claim in the token. This isn't correct as we
> permission checks
> > based on the authenticated client, not the token.
> >
> > So I'll have to create a new Identity type that either wraps the
> service
> > account or ClientModel and sets the "kc_client_id" property.
> >
>
> Our policy evaluation engine is based on the claims within the
> token. The
> "issueFor" is basically the "azp" claim from OIDC. In fact, we
> don't even
> need that "kc_client_id". We could make this configurable though,
> and let
> users decide whether they want to check the "authenticated client"
> or "azp"
> ?
>
> Btw, I'm about to finish UMA Grant Type, one of the changes I'm
> doing for
> UMA 2.0. My changes will conflict with yours. Are you going to
> merge your
> changes soon ?
>
> Another thing I noticed is that maybe we could have a SPI for
> custom grant
> types. What you did and what I'm doing may justify a specific SPI for
> plugging custom grant types. Maybe too much, but maybe a nice to have.
>
>
> >
> >
> > Bill
> >
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