UserManager.getRemoteUsername() returns null (in some context) despite being authenticated

UPDATE: As of UPM 2.14.2+, this bug prevents users from installing plugins through UPM in addition to the previous "anonymous" audit log behavior. See the comments below for more information.

When upgrading UPM 2.0 tests to run against Bamboo 3.4 (instead of Bamboo 3.4-rc2), I noticed a test fail. I tracked it down to Bamboo's SAL implementation of UserManager.getRemoteUsername() returning null when running in a transaction (TxTemplate) inside a Callable executed by an executor created by ThreadLocalDelegateExecutorFactory. I spent some time trying to generate a minimal reproducer, but the simple case was working fine for me.

What I can tell you is that this functionality was working OK with Bamboo 3.4-rc2 but broke in the Bamboo 3.4 release. To reproduce, you can check out r132786 of UPM. If you want to run Bamboo+UPM 2.0 from the UPM tree, build everything with mvn clean install -DskipTests, then run mvn amps:debug -Pbamboo34 -Dproduct=bamboo from the integration-tests directory.

If you install a plugin via UPM UI and then check the Audit Log, you'll see that the log entry is attributed to "anonymous" but should be "admin" (or whoever the current user is).

This issue corresponds to UPM-1521.