[keycloak-dev] Wildcard for Valid Redirect URI Hostname

Stian Thorgersen sthorger at redhat.com
Tue Sep 20 02:20:46 EDT 2016

I appreciate this feature might be useful, so there's no need to discuss
that aspect. The only issue I have with this PR is with regards to security
and especially as it enables doing the "wrong" thing.

With regards to redirect URIs with confidential clients they are still
important, but not quite as important as they are for public client. This
means redirect URIs can typically be more flexible with confidential
clients without a significant risk.

For public clients it's very important to lock these down as much as
possible as they are the ONLY way to prevent malicious clients to gain
access to the SSO session. This means we should actually tighten the
requirements for redirect URIs not further relax them. For public clients
the redirect URIs:

* Should be as specific as possible. We should only allow wildcard in the
path. I believe we should introduce this for both public and confidential
* Require HTTPs unless it's http://localhost. This is not so easy in
development, so maybe we should have an option to run the server in
"unsafe" mode for developers.

Here's a quote from the OIDC spec around this:

*"REQUIRED. Redirection URI to which the response will be sent. This URI
MUST exactly match one of the Redirection URI values for the Client
pre-registered at the OpenID Provider, with the matching performed as
described in Section 6.2.1 of [RFC3986] (Simple String Comparison). The
Redirection URI SHOULD use the https scheme; however, it MAY use the http
scheme, provided that the Client Type is confidential, as defined in
Section 2.1 of OAuth 2.0, and provided the OP allows the use of http
Redirection URIs in this case. The Redirection URI MAY use an alternate
scheme, such as one that is intended to identify a callback into a native

Looking at your comments on the PR it worries me slightly that you have a
shared client for a "library". A library is not a client. A client is an
instance of an application. Sharing the client will have impact on audit,
what clients a user believes they are authenticated to. With regards to
wildcard to allow any subdomains that is scary as your allowing any piece
of code running on any subdomain within your domain to authenticate via
that particular client. That could be an infected forum, something any user
has executing, etc.. As long as the redirect URI permits it an application
can obtain a token for a client for a user that is authenticated without
the user knowing about it. Unless you enable consent that is, but if the
user used the "real" client they would have given consent and the malicious
client on a different subdomain can take advantage of it.

In summary my opinion is that we can't accept this PR and that we further:

* Allow wildcard only in path. This is actually still looser than the OIDC
spec mandates as it requires a simple string comparison.
* Require HTTPS (or custom scheme) for public clients. We may need a
development mode that disables this.

On 19 September 2016 at 16:50, Josh Cain <josh.cain at redhat.com> wrote:

> Per KEYCLOAK-3585: <https://issues.jboss.org/browse/KEYCLOAK-3585>
> Currently, valid redirect URI hostnames allow for wildcards at the end
> like so:
> http://www.redhat.com/*
> I'm managing several environments where clients need 'n' number of
> available redirect URI's with different hostnames, I.E.
> http://developer1.env.redhat.com
> http://developer2.env.redhat.com
> http://developer3.env.redhat.com
> Would really help to have the ability to wildcard hostnames too, I.E.:
> http://*.env.redhat.com
> I've submitted #3241 <https://github.com/keycloak/keycloak/pull/3241> to
> address this issue, but there seem to be some concerns about allowing
> wildcards in other parts of the URL.  See the PR for a more fleshed out
> discussion, but wanted to start a thread here on the mailing list.
> Particularly with respect to:
>    - Does anyone have need of this feature or would find it useful?
>    - Should this kind of wildcard be allowed as a configuration option by
>    Keycloak?
> Josh Cain | Software Applications Engineer
> *Identity and Access Management*
> *Red Hat*
> +1 256-452-0150
> _______________________________________________
> keycloak-dev mailing list
> keycloak-dev at lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/keycloak-dev
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