Hi,

The current nnimap/auth-source combo does not seem to support multiple
IMAP accounts on the same host/port.  How about adding `nnimap-username'
server parameter to user can specify username like:

 (setq gnus-secondary-select-methods
       '((nnimap "ueno"
                 (nnimap-address "example.org")
                 (nnimap-username "ueno"))
         (nnimap "daiki"
                 (nnimap-address "example.org")
                 (nnimap-username "daiki"))))

Here is a quick patch.