https://bugzilla.redhat.com/show_bug.cgi?id=783308 shows gnome-shell crashing because the NMSecretAgent base class is asking it to cancel a request that ShellNetworkAgent doesn't know about.

The only way it should be possible for this to happen is if ShellNetworkAgent removes a request from priv->requests without calling request->callback() first, and AFAICT, that never happens. So, I don't know what's going on here.

Presumably the request is not actually active at the time the user restarts NM. Rather, it was started at some point in the past, and the shell believed it completed, but libnm-glib never got the memo.

Anyway, this patch might avoid the crash (assuming that the problem is as described above, rather than just being memory corruption somewhere). Yes, it leaks memory, but not much, and you're not supposed to hit this case anyway. (Then again, it's also possible that the crash doesn't exist in 3.4, although there doesn't seem to be anything relevant changed in either gnome-shell or NM that would affect this. If anything, it would be the VPN-related changes in ShellNetworkAgent, but the code looks correct both before and after...)