SQLite driver and auth-worker credentials

I want to use SQLite database as storage for auth and user databases. I've encountered two problems here:

(1) There is no way to open SQLite database read-only (via sqlite3_open_v2() call with SQLITE_OPEN_READONLY flag). It looks bad. I don't need (and want) to give dovecot rights to write to this database.

(2) I've created system group "hostingdb", added "dovecot" user to it and gives 660 rights to database file, but still "auth-worker" could not open database and complains to log file. Now I'm set "user = root" for auth-worker, but I don't like it! Why auth-worker doesn't belong to "hostingdb" group?

-- // Black Lion AKA Lev Serebryakov