MongoDB Java Driver v2.9.0
MongoDB v2.2.0 (running as a Replica Set)

We were trying to upgrade MongoDB to v2.2.0 from v2.0.3, after upgraded the
java driver to v2.9.0 . We found that our MapReduce task (which takes input
from a collection in someAppName-TESTING DB, and outputs to a temp
collection in someAppName_temp DB) started to fail due to
unauthorization issue:

Mon Sep 10 07:30:08 [conn391]  authenticate db: someAppName-TESTING {
authenticate: 1, user: "someUsername", nonce: "a26a0d7e6b8089b3", key:
"someKey" }
Mon Sep 10 07:30:09 [conn391] mr failed, removing collection :: caused by
:: 10057 unauthorized db:someAppName_temp ns:
someAppName _temp.tmp.mr.resultsCollection_63_inc lock type:1 client:
someIPAddress

I found that there is a checkAuth(DB db) method on the DBPort class, and I
realized that the MongoDB driver might has a bug that it won't check for
authentication of the Output db for MapReduce. Is there anything I can do
to ensure that the output db is authenticated before performing a
MapReduce? Thank you.

I haven't looked at other drivers, but I suppose this is a driver design
issue (2 levels of authentication cache, one on the DB level, and the other
on the DBPort level). The driver has a isAuthenticated() method on DB
class, which checks whether the db has been successfully authenticated
previously. On the other hand, each connection requires authentication to
the db if we are to execute any command on that db, which is why there is a
checkAuth(db) method on DBPort class. But the drawback is now exposed that
if the output db of MapReduce is not the same as the one you issue the
MapReduce command on, DBPort will not be able to authenticate against the
output db.

I've figured out a workaround that I have to add a method to DB class to
enforce authentication, such that before sending out the MapReduce command,
I can ensure my temp db is authenticated for that connection.  

created a JIRA <https://jira.mongodb.org/browse/JAVA-651>