[keycloak-dev] token exchange

Tue Aug 15 02:50:27 EDT 2017

First of all I'm not arguing against token exchange service. It's a very
useful thing IMO and I can see loads of use-cases for it. I'm just
wondering about how usable it will be for the CLI tool and I'm worried
about how complicated it would be to setup. If the ID token was signed that
could serve as a the "identity cookie" for a CLI SSO session (if ID token
is not suitable we could introduce some sort of identity token that can be
used by direct grant to allow SSO sessions). Using direct grant you can
then easily obtain a token for a specific client by just passing a valid
"identity cookie" same way as the web browser does. Is that not simpler to
setup and use?

On 14 August 2017 at 15:42, Bill Burke <bburke at redhat.com> wrote:

> 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> wrote:
>
>> On Mon, Jul 31, 2017 at 1:54 PM, Bill Burke <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> 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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