[keycloak-dev] token exchange
Bill Burke
bburke at redhat.com
Tue Aug 15 11:32:59 EDT 2017
I would be worried about the security implications of allowing an ID
token as a way to obtain access. If you have even one client in the
domain that is not fully trusted then you are toast. So how is it set
up to make things easy? One "master" client is defined in realm. That
client is given permission to obtain exchange for anything. That client
is marked as confidential. Generic CLI tool is configured with client id
and secret of "master" client.
On 8/15/17 2:50 AM, Stian Thorgersen wrote:
> 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
> <mailto: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
>> <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
>> >
>> _______________________________________________
>> keycloak-dev mailing list
>> keycloak-dev at lists.jboss.org
>> <mailto:keycloak-dev at lists.jboss.org>
>> https://lists.jboss.org/mailman/listinfo/keycloak-dev
>> <https://lists.jboss.org/mailman/listinfo/keycloak-dev>
>>
>>
>
>
More information about the keycloak-dev
mailing list