[keycloak-user] Token Exchange AWS Cognito & Keycloak

Matteo Restelli mrestelli at cuebiq.com
Mon Apr 15 04:08:34 EDT 2019 

Hi Pedro,
Thank you for your replies and your patience :)
My answers inline below ;)

Have a nice day,
Matteo

On Fri, Apr 12, 2019 at 4:53 PM Pedro Igor Silva <psilva at redhat.com> wrote:

>
>
> On Fri, Apr 12, 2019 at 11:28 AM Matteo Restelli <mrestelli at cuebiq.com>
> wrote:
>
>> Thank you Pedro,
>> My answers (and questions) inline below ;)
>>
>> Thank you!
>> Matteo
>>
>> On Fri, Apr 12, 2019 at 3:20 PM Pedro Igor Silva <psilva at redhat.com>
>> wrote:
>>
>>> Thanks. Now it is more clear.
>>>
>>> Answers inline below.
>>>
>>>
>>> On Fri, Apr 12, 2019 at 7:29 AM Matteo Restelli <mrestelli at cuebiq.com>
>>> wrote:
>>>
>>>> Hi Pedro,
>>>> i'll try to reply to your questions:
>>>>
>>>> - We've configured Cognito as an identity provider in Keycloak,
>>>> importing the configuration via the OIDC discovery-configuration endpoint.
>>>> At this point we needed to introduce the clientID & secret, so we've
>>>> created a new confidential client inside AWS Cognito and used its id
>>>> &secret in the Keycloak's Identity provider config
>>>>
>>>
>>>> - We've set the permission & policy about token exchange feature to our
>>>> Keycloak client
>>>>
>>>> - The SRP flow leverages the SRP authentication protocol (so basically,
>>>> no password is sent to the server). The result of this flow is a couple of
>>>> JWT tokens (access and id token), but the access token doesn't respect the
>>>> OIDC rules (it doesn't contain the openid scope). This last point is what
>>>> make the token exchange process impossible (this because, during the
>>>> process, Cognito replies that "the token doesn't contain the openid
>>>> scope"). About that i want to highlight the fact that these problems are
>>>> entirely Cognito related: if we use a standard OAuth2 Flow (like
>>>> Authorization code grant or implicit) the process works as expected.
>>>>
>>>
>>> I see now. In this case, I think you should try to include somehow the
>>> openid scope in the access token so that Cognito can process it. I guess
>>> this error is returned when the broker is invoking the user endpoint  on
>>> Cognito? based on the OIDC user info endpoint definition, the endpoint
>>> should accept access tokens.
>>>
>>
>> Yeah unfortunately we're stuck with this option, because Cognito is
>> lacking support on adding this scope to the token (especially this is
>> caused by the Amplify.js library provided by AWS, which is the one we're
>> using to implement the SRP flow). Yes, the error is returned from Cognito
>> when Keycloak contacts the provider to validate the token.
>>
>
>>
>>
>>>
>>>
>>>> - Since the SRP flow enables us to use a self-hosted login page which
>>>> doesn't send the password directly to the server, we've tried to find other
>>>> solution. So we've tried to provide to the token exchange endpoint the id
>>>> token, changing some parameters of the HTTP call. And at this point
>>>> something unexpected for us happened: the token exchange process works also
>>>> providing the id token. Here's the reason of my first flow of questions: is
>>>> this behaviour expected? Is the "exchange with id token" approach a
>>>> feasible and good one? Or is completely a bad approach?
>>>>
>>>> - Since using this flow (SRP) force us to provide the id token to our
>>>> backend side, here comes the other flow of questions :). From an OIDC point
>>>> of view, can be a right approach accessing a backend resource from a single
>>>> page application, using an id token? I've always read that if you want to
>>>> access to a backend resource, from a client application, is better to use
>>>> the access token, because the id token contains a lot of user informations
>>>> and must be used only by the client application.
>>>>
>>>>
>>> It is fine to use id_token (or any other format supported by the server
>>> that can be specified via subject_token_type) when doing the exchange.
>>>
>>> However, here is the interesting part. If you look our documentation we
>>> should only support "access_token" and "jwt" as a subject_token_type. But
>>> the implementation can also handle "id_token". The reason why "id_token"
>>> works is that the validation of the token is done locally by Keycloak,
>>> differently than when you are using an access_token where a request will be
>>> sent to the user info endpoint on Cognito.
>>>
>>
>> Oh! That's really interesting! :)
>> About this point, in your opinion it will be feasible to call the token
>> exchange endpoint every time a request comes to our backend side? Imagine
>> this scenario:
>>
>> - User authenticates to Cognito via the Spa app
>> - Spa app calls backend services (tipically contacting a gateway)
>> - Gateway performs the token exchange on keycloak
>> - Gateway forwards the request (adding the new access token in place of
>> the Cognito one) to the underlying microservices...
>>
>> Do you see any performance issues? Does Keycloak caches something during
>> the token exchange process?
>>
>
> I would ask you to try it out and check latency and response times.
> Unfortunately, benchmarking is something we are lacking so we depend on
> feedback from the community.
>

> Maybe, another option you could consider is to aggregate your APIs so that
> your SPA doesn't need to interact with multiple backend services ? Where
> this API aggregator would be 1:1 mapped to your client and responsible for
> all exchanges to access downstream services.
>

So the main idea is to put a gateway in front of all the microservices, so
it will be the one who performs the token exchange process. To avoid
performance issues we can think about a caching mechanism but in this way
we need to investigate more (we're just evaluating the various options
right now ;) ). By the way, IMHO, if a user calls the gateway 300 times in
3 minutes there's no reason to perform the token exchange process at every
call.



>
> Or you could eventually use different scopes to gain access to these
> different services and still use the same token obtained by the client
> during the authentication. There is a caveat here regarding audience
> though, so you could maybe include some audience that logically represent
> your different APIs.
>

So, if i understood correctly:
- Client contacts gateway with a Cognito access token
- Gateway performs the token exchange process
- Depending on which service needs to be called, the gateway requests
scopes to Keycloak with the access token minted by Keycloak. Is this right?
Or requesting scopes is done in the token exchange process?

So i've some concepts regarding scopes that i read around on the Internet,
and for what i've understood, a scope represents what an oauth2 client can
do:
- You need to call service A, perform a read operation
- You request the custom scope read_service_a

I'm lacking the link between those scopes and the authorization part. How
are they linked with the authorization services in Keycloak? If a user
isn't authorized to do something, will never receive the related scope? Or
are they completely separated concepts?

The audience part is fine for me, also here for what i've understood, the
audience represents the "target" resource protected by the server. Am i
right?


>
>>
>>
>>>
>>> Regarding your last question, no it is not a good practice to use
>>> id_token for bearer token authorization. In addition to privacy concerns
>>> (which is not really different than when using JWTs in access tokens), ID
>>> Token is about carrying the authentication context with specific
>>> constraints. For instance, the audience is the client, not the backend. The
>>> lifetime of ID Token is shorter as they are mainly important to
>>> authenticate the user into a client, etc.
>>>
>>> So, you are right. You should try to use access tokens.
>>>
>>
>> Ok thank you for the explanation. We'll try to use access tokens
>> (probably we'll stop using the SRP flow in favour of an OAuth2 flow like
>> Authorization Code Grant with PKCE (which is the one recommended for public
>> Single page Applications)
>>
>
> +1
>
>
>>
>>
>>
>>
>>>
>>>
>>>> - Here's the curl of the token exchange process with the access token
>>>> (i'm omitting some infos):
>>>>
>>>> curl -X POST \
>>>> -d "client_id=test" \
>>>> -d "client_secret=<client_secret>" \
>>>> --data-urlencode
>>>> "grant_type=urn:ietf:params:oauth:grant-type:token-exchange" \
>>>> -d "subject_issuer=<alias_of_the_identity_provider_in_keycloak>" \
>>>> -d "subject_token=<access_token>" \
>>>> --data-urlencode
>>>> "subject_token_type=urn:ietf:params:oauth:token-type:access_token" \
>>>> -d "audience=test" \
>>>> http://localhost:8080/auth/realms/
>>>> <realm_name>/protocol/openid-connect/token
>>>>
>>>>
>>>> - Here's the curl of the token exchange process with the id token (i'm
>>>> omitting some infos):
>>>>
>>>> curl -X POST \
>>>> -d "client_id=test" \
>>>> -d "client_secret=<client_secret>" \
>>>> --data-urlencode
>>>> "grant_type=urn:ietf:params:oauth:grant-type:token-exchange" \
>>>> -d "subject_issuer=<alias_of_the_identity_provider_in_keycloak>" \
>>>> -d "subject_token=<id_token>" \
>>>> --data-urlencode
>>>> "subject_token_type=urn:ietf:params:oauth:token-type:id_token" \
>>>> -d "audience=test" \
>>>> http://localhost:8080/auth/realms/
>>>> <realm_name>/protocol/openid-connect/token
>>>>
>>>> Let me know if you need more infos.
>>>>
>>>> Thank you again,
>>>> Matteo Restelli
>>>>
>>>> On Wed, Apr 10, 2019 at 3:40 PM Pedro Igor Silva <psilva at redhat.com>
>>>> wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> So you are doing external to internal exchange. It is not clear to me
>>>>> how you configured AWS Cognito as an identity provider and what/how the SRP
>>>>> flow works. Could you provide more details, please? Is the token issued by
>>>>> Cognito a JWT ?
>>>>>
>>>>> In addition to that, how your token exchange request looks like when
>>>>> using both id_token and access_token as a subject_token ?
>>>>>
>>>>> On Wed, Apr 10, 2019 at 9:56 AM Matteo Restelli <mrestelli at cuebiq.com>
>>>>> wrote:
>>>>>
>>>>>> Any news on that?
>>>>>>
>>>>>> Thank you!
>>>>>> Matteo
>>>>>>
>>>>>> =============================
>>>>>>
>>>>>>
>>>>>> Hi all,
>>>>>> We're using AWS Cognito as our Identity provider for our platform.
>>>>>> We're
>>>>>> trying to use an internal instance of Keycloak, in order to check the
>>>>>> possibility to use KC for authorization purposes (this because
>>>>>> Keycloak has
>>>>>> a wonderful and powerful authorization system that fulfill our needs,
>>>>>> and
>>>>>> for that i want to say you "Thank you very much" :) ). For this
>>>>>> reason we
>>>>>> want to use the token exchange feature of Keycloak.
>>>>>> More specifically we want to follow this flow:
>>>>>>
>>>>>> - User authenticates on AWS Cognito via SRP auth flow (which
>>>>>> basically is
>>>>>> not a standard OIDC/OAuth2 authentication flow)
>>>>>> - User sends the access token to contact the backend service and, in
>>>>>> the
>>>>>> middle, this token is translated to an internal one, minted by
>>>>>> Keycloak
>>>>>>
>>>>>> If we provide the AWS Cognito access token to the token exchange
>>>>>> endpoint,
>>>>>> with the subject_token_type parameter set to
>>>>>> "urn:ietf:params:oauth:token-type:access_token", an error is returned
>>>>>> stating that the access token doesn't contain the "openid" scope.
>>>>>> Despite
>>>>>> this we've tried another way, providing the id token to the token
>>>>>> exchange
>>>>>> endpoint with the subject_token_parameter set to
>>>>>> "urn:ietf:params:oauth:token-type:id_token", and we discovered that
>>>>>> this
>>>>>> alternative way works. So, my questions are:
>>>>>>
>>>>>> - Is the "exchange with id token" approach a feasible and good one?
>>>>>> Or is
>>>>>> completely a bad approach?
>>>>>> - From an OIDC point of view, can be a right approach accessing a
>>>>>> backend
>>>>>> resource from a single page application, using an id token? I've
>>>>>> always
>>>>>> read that if you want to access to a backend resource, from a client
>>>>>> application, is better to use the access token, because the id token
>>>>>> contains a lot of user informations and must be used only by the
>>>>>> client
>>>>>> application
>>>>>>
>>>>>> Thank you very much,
>>>>>> Matteo
>>>>>>
>>>>>>
>>>>>> PS:  As a side note, i want to clarify that if we follow an
>>>>>> authorization
>>>>>> code grant flow, or an implicit flow, during the authentication
>>>>>> against AWS
>>>>>> Cognito, the access token exchange works as expected. So this means
>>>>>> that
>>>>>> the problem is related to the shape of the token released by Cognito.
>>>>>>
>>>>>> --
>>>>>>
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>>>>>>
>>>>>
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