pam_env -- why is it an auth module?

[Jeffrey Layton <jtlayton@poochiereds.net>]

I've been looking at the pam configuration on some of my debian boxes.
I'm trying to set up pam_winbindd, but am going to have some issues with
stacking.

I saw that pam_env is enabled as an auth module, and saw this blurb in
its config file:

# The original idea for this came from Andrew G. Morgan ...
#<quote>
#   Mmm. Perhaps you might like to write a pam_env module that reads a
#   default environment from a file? I can see that as REALLY
#   useful... Note it would be an "auth" module that returns PAM_IGNORE
#   for the auth part and sets the environment returning PAM_SUCCESS in
#   the setcred function...
#</quote>

My question is -- why does this need to be an "auth" module? It would
seem to make more sense for it to be a "session" module.

Can anyone shed light on the reasoning behind the above comment?

-- Jeff