[Freeipa-devel] FreeIPA and wildcard certificates

[Martin Kosek]

On 02/09/2017 10:44 PM, Fraser Tweedale wrote:
> 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.

Right, it supports this. But then issuing the certificate and renewal is a
responsibility of app developer, AFAIK. I do not think if OpenShift has all the
needed hooks to do this automatically and call certmonger for example.

TLDR; adding a support of certmonger and issuing a certificate for every new
application is a whole another degree of complexity than just issuing a
Wildcard certificate for the router. I am not saying it should not be done, I
am just saying that being able to generate a wildcard certificate with FreeIPA
would let us integrate with OpenShift much better than now and with (hopefully)
low effort involved, i.e. faster.

> 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 :)

We do not need to jump on implementing it right away, you already have a lot on
your plate. Right now, I must just want to know:

- is there any way how I can generate wildcard cert with current FreeIPA, using
a custom certificate profile. I assume the answer is no.

- how complex would it be to add support of Wildcard certificate support to
FreeIPA (rough scope).

Thanks,
Martin