search text on the terminal output

Ctrl+a (default screen command prefix), [ (enter copy mode) followed by ?SEARCH_TEXT seems to work. Press n to go to the next occurrence. From there, you can copy words, lines, regions, etc to dump into files or paste later on (with Ctrl+a, ]).

If you use Konsole (KDE terminal emulator), you can use Ctrl + Shift + F. This might work also in other (Linux) terminal emulators.

Edit:
@sumit reports this works also in Gnome Terminal.
@vdicarlo reports this also works in XFCE4 Terminal.

You can use grep after the grails command: grails run-app | grep "user authorities". However, you will have to re-run your command.