[Freeipa-devel] certmonger everywhere

Wed Dec 16 08:17:09 UTC 2015

On 16.12.2015 08:54, Martin Kosek wrote:
> On 12/16/2015 08:09 AM, Jan Cholasta wrote:
>> On 16.12.2015 01:40, Fraser Tweedale wrote:
>>> On Tue, Dec 15, 2015 at 04:23:33PM +0100, Martin Kosek wrote:
>>>> On 12/15/2015 08:54 AM, Jan Cholasta wrote:
>>>>> Hi,
>>>>>
>>>>> recently I and David discussed the direction of installers with
>>>>> regard to
>>>>> requesting certificates. Currently there are four (!) different
>>>>> ways of
>>>>> requesting certificates in the installer [1][2][3][4]. We would
>>>>> like to reduce
>>>>> it to one.
>>>>>
>>>>> Since all the certificates are tracked by certmonger and certmonger
>>>>> already
>>>>> knows how to request certificates from Dogtag (and other CAs), we
>>>>> believe that
>>>>> all certificates should be requested using certmonger.
>>>>>
>>>>> Taking our meditation further, we thought "Why not use certmonger
>>>>> for the
>>>>> cert-request command as well?" What is the benefit, do you ask?
>>>>>
>>>>>   a) single code path for requesting certificates (seriously, the
>>>>> current
>>>>> state
>>>>> is ridiculous)
>>>>>
>>>>>   b) use any CA supported by certmonger as the IPA CA (i.e. Let's
>>>>> Encrypt [5],
>>>>> once certmonger gains support for it)
>>>>>
>>>>>   c) automate external CA install, using any CA supported by
>>>>> certmonger [6]
>>>>>
>>>>>   d) support multiple different CAs at once (generalization of the
>>>>> Sub-CA
>>>>> feature)
>>>>>
>>>>>   e) uniform configuration on clients (configure once, use forever,
>>>>> even for
>>>>> CA-less)
>>>>>
>>>>> The idea is to store configuration for the different CAs in LDAP
>>>>> and have
>>>>> cert-request redirect requests to a proper CA helper according to that
>>>>> configuration. This would require a new certmonger D-Bus method to
>>>>> call a CA
>>>>> helper without associated certificate storage, but that should be
>>>>> rather easy
>>>>> to add. In return, it would be possible to do all of the above.
>>>>>
>>>>> Note that this should not conflict with tighter integration with
>>>>> Dogtag
>>>>> (profiles, ACLs, etc.).
>>>>>
>>>>> Comments are welcome.
>>>>>
>>>>> Honza
>>>>>
>>>>> [1]
>>>>> <https://git.fedorahosted.org/cgit/freeipa.git/tree/ipapython/certmonger.py#n305>
>>>>>
>>>>>
>>>>> [2]
>>>>> <https://git.fedorahosted.org/cgit/freeipa.git/tree/ipaserver/install/certs.py#n329>
>>>>>
>>>>>
>>>>>
>>>>> [3]
>>>>> <https://git.fedorahosted.org/cgit/freeipa.git/tree/ipaserver/install/certs.py#n355>
>>>>>
>>>>>
>>>>>
>>>>> [4]
>>>>> <https://git.fedorahosted.org/cgit/freeipa.git/tree/ipaserver/install/cainstance.py#n878>
>>>>>
>>>>>
>>>>>
>>>>> [5] <https://fedorahosted.org/freeipa/ticket/5431>
>>>>> [6] <https://fedorahosted.org/freeipa/ticket/5317>
>>>>
>>>> Interesting idea! I would be definitely interested to hear what
>>>> Fraser, Rob or
>>>> Simo thinks here.
>>>>
>>> For the installer cases, +1 from me.
>>>
>>> For the general cert-request case, currently Certmonger calls `ipa
>>> cert-request' using host credentials (Kerberos), and IPA framework
>>> does some validation (e.g. ensure CN and altNames correspond to
>>> subject principal), before requesting cert from Dogtag using RA
>>> Agent credentials (TLS client cert).
>>>
>>> There are a few things that have to happen before Certmonger can
>>> request certs directly from Dogtag, in IPA scenario:
>>>
>>> 1. support SNPEGO authentication in Dogtag (work has started)
>>>
>>> 2. perform all validation that IPA framework currently performs in
>>>     Dogtag, or make the validation no longer required by pulling cert
>>>     data straight from LDAP according to the profile.
>>>
>>> 3. Requestor credentials must be delegated to Certmonger so that the
>>>     correct principal is used to talk to Dogtag.  Presumably this would
>>>     be S4U2Proxy constrained delegation with host/<hostname> as
>>>     impersonator and Dogtag service principal as target.
>>>
>>> At that point `ipa cert-request' can become a client-side command
>>> that merely configures Certmonger to request the cert.
>>
>> I'm not proposing to change cert-request to a client side command - I'm
>> proposing to change the way cert-request is handled *on the server*.
>
> I do not think Fraser was suggesting to change cert-request to a client
> side command. More below.

See 3 paragraphs above: "... `ipa cert-request' can become a client-side 
command...".

>
>> This way
>> we can keep all the configuration on the server and make changes to it
>> without
>> having to reconfigure all clients.
>>
>> This is how I envision the workflow:
>>
>>   1. client requests a certificate with "getcert request", using "IPA"
>> as the
>> CA and, optionally, a string identifying the sub-CA (for the lack of
>> better term)
>>
>>   2. "getcert request" forwards the request to certmonger over D-Bus
>> and exits
>>
>>   3. certmonger creates CSR for the request
>>
>>   4. certmonger executes the IPA CA helper to handle the request
>>
>>   5. the IPA CA helper calls the cert-request command on the server
>> over RPC,
>> using local host credentials for authentication
>>
>>   6. cert-request on the server validates the request
>
> Right. These are the steps that happen already, AFAIK.

Correct.

>
>>   7. cert-request fetches the configuration for the specified sub-CA,
>> or the
>> default sub-CA if none was specified, from LDAP
>>
>>   8. cert-request forwards the request to the certmonger CA helper
>> specified in
>> the LDAP configuration over D-Bus (this is the D-Bus method that
>> currently does
>> not exist and needs to be implemented)
>>
>>   9. certmonger executes the specified CA helper to handle the request
>>
>>   10. the CA helper requests the certificate from the CA and returns
>> either the
>> certificate, wait delay or error
>>
>>   11. certmonger returns the result back to cert-request
>
> These steps are subject to Fraser's question (and I am curious too), i.e.:
>
> - how is authentication done? certmonger runs with FreeIPA server host
> principal.

We are on the server, so the RA agent cert is used to authenticate to 
Dogtag as usual, and whatever authentication is configured for other CAs 
is used for other CAs.

> - how will we handle 3-step certificate request, i.e.:
>    - certificate is requested and in moderation/wait queue
>    - request have to be acked by Dogtag administrator (we do not have
> API yet)
>    - client should be able to ask for generated certificate

This is not really related to my proposal, since we have to figure this 
out for our Dogtag IPA CA anyway, but the CA helper can return a wait 
delay in this case, so certmonger can poll the request until it is approved.

>
>>   12. cert-request returns the result back to IPA CA helper on the client
>>
>>   13. the IPA CA helper on the client returns the result back to
>> certmonger
>>
>>   14. if the result was wait delay, certmonger waits and then retries the
>> request from step 4, otherwise it stores the certificate or sets error
>> status
>>
>
> Right, 12-14 is again the standard flow. Good summary of the steps!

-- 
Jan Cholasta