[Pki-devel] SPNEGO for Dogtag

[Fraser Tweedale]

Hi all,

Just an update on my investigations of doing SPNEGO authn to
Dogtag/Tomcat and a summary of what I think I'll need to do to get
it going.

Even for a trivial app configuring Tomcat to do SPNEGO is pretty
awful.  I made some notes[1] on this and I'll turn that into a blog
post later, once I have a Realm story to go with it (I'm thinking
mod_lookup_identity for Tomcat; more on that below).

[1] https://github.com/frasertweedale/notes-redhat/blob/master/tomcat.rst


The unfortunate case is that the `Authenticator' interface does not
chain, hence we already have our own `SSLAuthenticatorWithFallback'
authenticator valve implementation which we use to fall back to
Basic authentication when there is no client certificate.

I see two general approaches to the "multiple authentication
options" problem.

a) a "parallel deployment" in a separate <Context> where we host the
app in parallel at '/<subsystem>/spnego/...' or
'/spnego/<subsystem>/...' and use the `SpnegoAuthenticator' valve.
This is a pretty "heavyweight" approach and I believe sessions from
one do not flow to the other, and a whole separate CMS application
is running.  So it does not seem viable.

b) `SSLAuthenticatorWithFallback' becomes "SSL or SPNEGO or Basic"
valve.  The problem here is that protocol-wise there is no
indication on initial request whether client can do SPNEGO or not,
so it is not clear how server should respond.  An example of how
this could be resolved is the client providing a '?spnego=1' query
param; ugly but it should work, and w.r.t. REST API the client need
only do it on /rest/account/login and use their session cookie
thereafter, so I don't think it is too onerous.

So it looks like (b) but if someone can suggest another approach I'm
listening!


As for the Realm, the current implementation is a bit unorthodox -
we use our own ProxyRealm class and "inject" a PKIRealm into it.
I'm not sure why this approach is needed becaues PKIRealm does not
need any configuration either on instantiation or afterwards.

I think the best approach here would be to use CombinedRealm[2] and
add PKIRealm as well as whatever other Realms are needed.  For IPA
usage I am leaning toward the mod_lookup_identity approach; given
principal name look up roles (groups) via D-Bus.

[2] https://tomcat.apache.org/tomcat-7.0-doc/config/realm.html#Combined_Realm_-_org.apache.catalina.realm.CombinedRealm

Jan: does this approach make sense to you and do you know of any
projects to do this with Tomcat already?

Ade: what sort of behaviour do you need in the Realm for the Barbian
use case?


Any and all feedback welcome.

Thanks,
Fraser