When compiling against the C++ driver headers in a project which uses -Woverloaded-virtual, gcc complains as follows:

cc1plus: warnings being treated as errors
In file included from /tmp/mongo-tmp-install/include/mongo/client/connpool.h:21,
from db/AccessControl.cc:3:
/tmp/mongo-tmp-install/include/mongo/client/dbclient.h: At global scope:
/tmp/mongo-tmp-install/include/mongo/client/dbclient.h:390: error: 'virtual bool mongo::DBClientWithCommands::auth(const std::string&, const std::string&, const std::string&, std::string&, bool)' was hidden
/tmp/mongo-tmp-install/include/mongo/client/dbclient.h:899: error: by 'bool mongo::DBClientPaired::auth(const std::string&, const std::string&, const std::string&, std::string&)'

Shadowing virtual functions like this is typically pretty bad practice, since it makes it very non-obvious at the call-site what is going on. Also, -Woverloaded-virtual is a fairly common warning flag to enable.