[Building Sakai] LTI - callbacks

[George Pipkin]

Hi -

    I am evaluating the LTI capabilities within Sakai as they relate to 
the ability of a provider to
call back to sakai and obtain things like an Roster in xml form.  I have 
discovered a good
deal of code in v2.8 and the current (v2.9?) trunk to support this, and 
I have been trying to test
it.  I have gained a basic understanding of how it works.  You have to 
include a property in sakai.properties
(basiclti.roster.enabled=true) and check the checkbox for rosters to 
even get the ID and the url to call
back in the POST that is sent down by Basic LTI.  I am running v2.8 of 
sakai.

    My callback makes it back to the proper place, and I've figured out 
that I need to send a number of
things back such as oauth_consumer_key, oauth_nonce, oauth_timestamp, 
lti_version,
oauth_signature, oauth_signature_method.  However, I'm getting hung up 
validating the signature because
an object called the accessor needs something called the token secret, 
and that gets set to
null when OAuthAccessor is created (line 317 of ServiceServlet). And I 
can't
figure where or how it's supposed to get populated.

    I have a few questions -

1) Is this even supposed to work in v2.8, or is v2.9 the only thing in 
which the code actually works, notwithstanding
the presence of code in v2.8 to support this functionality ?

2) Is there something I need to supply in the callback request that 
causes the token secret to be populated
properly.  I've been poking around Chuck's code - 
tool_provider_outcome.php on Google code's IMS area,
and I assume that is supposed to work, but I don't see it yet.

3) Can anybody point me to some example code ? Again, I think Chuck's 
code on Google might be this, but
is there anything out there that does exercise any one of these 1.1 
callbacks that would illuminate my
investigation.

                          - George Pipkin
                             U.Va.