[Freeipa-devel] FreeIPA and wildcard certificates

[Fraser Tweedale]

On Thu, Feb 09, 2017 at 08:37:23AM +0100, Martin Kosek wrote:
> On 02/09/2017 02:12 AM, Fraser Tweedale wrote:
> > On Wed, Feb 08, 2017 at 10:19:54AM +0200, Alexander Bokovoy wrote:
> >> On ke, 08 helmi 2017, Martin Kosek wrote:
> >>> Hi Fraser and the list,
> >>>
> >>> I recently was in a conversation about integrating OpenShift with FreeIPA. One
> >>> of the gaps was around generating a wildcard certificate by FreeIPA that will
> >>> be used in the default OpenShift router for applications that do not deploy own
> >>> certificates [1].
> >>>
> >>> Is there any way that FreeIPA can generate it? I was thinking that uploading
> >>> some custom certificate profile in FreeIPA may let us get such certificate...
> >>> Or is the the only way we can add it by adding a new RFE in FreeIPA, tracked in
> >>> [2]?
> >> Yes, we need a new RFE. There are checks in IPA that prevent wildcard
> >> certificates to be issued:
> >>
> >> - we ensure subject 'cn' of the certificate matches a Kerberos principal
> >>   specified in the request
> >>
> >> - we validate that host object exists in IPA when the Kerberos
> >>   principal is host/...
> >>
> >> We could lift off these two limitations for 'cn=*,$suffix' but there is
> >> still a need to apply proper ACLs when issuing the cert -- e.g. some
> >> object has to be used for performing access rights check. The wildcard
> >> certificate does not need to be stored anywhere in the tree, but a
> >> check still needs to be done.
> >>
> >> For example, for Kerberos PKINIT certificate which is issued to KDC we
> >> don't store public certificate in LDAP either but we do two checks:
> >> - a special KDC certificate profile is used to issue the cert
> >> - a special hostname check is done so that only IPA masters are able to
> >>   request this certificate
> >>
> >> For the wildcard certificate I think we could have following:
> >> - use a separate profile for the wildcard, associated with a sub-CA
> >> - hardcode CN default in the profile to always be 'CN=*, O=$SUB_CA_SUBJECT' so that
> >>   actual certificate ignores requested CN.
> >> - a special check to be done so that only wildcard-based subject
> >>   alternative names can be added to a wildcard certificate request
> >> - all Kerberos principal / hostname checks are skipped.
> >> - actual ACL check is done by CA ACL.
> >>
> > Issuing wildcard certs is a deprecated practice[1].  I am not
> > dismissing the needs of OpenShift (or PaaS/IaaS solutions in
> > general) but I'd like to have a discussion with them about how
> > they're currently dealing with certs and whether a different
> > direction other than wildcard certs is feasible.  Martin, who should
> > I reach out to?  Feel free to copy them into this discussion.
> 
> Right now, I am talking to a Solution Architect, i.e. someone who is building
> GAed solutions, not developers. This is not something we would change
> short-term anyway, this is how current OpenShift v2 or v3 behaves, despite the RFC.
> 
> While I understand why having certificate *.lab.example.com and using it for my
> lab machines is a bad idea and increases the attack vector, I do not see it
> that way for OpenShift. There, applications get URL like
> "<app-dom>.myopenshift.test" and all is routed by one entity, the OpenShift
> broker. So the key.cert is on one location, just serving different names that
> are provisioned with OpenShift.
> 
> I can understand that issuing a new certificate for every application
> provisioned by OpenShift and then renewing it complicates the design
> significantly. I am trying to be creative and see if current OpenShift could
> leverage FreeIPA CA and issue the broker cert, with current profile
> capabilities or with small change.
> 
I believe OpenShift supports per-application certificates (i.e. when
app developers/maintainers supply their own cert for a custom
domain).  So it might be possible in v2 or v3 to provision a cert
for every app.  An automated solution does not yet exist but that
doesn't mean it can't be built out of what's currently GA.

> > [1] https://tools.ietf.org/html/rfc6125#section-7.2
> > 
> > If we do go ahead with wildcard cert support in FreeIPA, some of my
> > initial questions are:
> > 
> > - For the OpenShift use case, what is the "parent" domain name and
> >   is it the same as the IPA domain name?  Is it a subdomain of the
> >   IPA domain name?
> > 
> > - Do we need to support issuing "*.${IPA_DOMAIN}"? i.e. wildcard
> >   cert under entire IPA domain name.
> > 
> > - Do we need to support issuing "*.${IPA_HOSTNAME}"?  i.e. wildcard
> >   certs under names of IPA host principals.
> 
> I do not know, but I can ask if it is important for you :-)
> 
It's important to know what I actually need to do if we proceed with
implementing this :)

Cheers,
Fraser