This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
So it seems to need a JDBCTemplate passed in to it, just like you did with the dataSource. Just create a bean with JDBCTemplate passing dataSource in to a contructor-arg. Then inject the jdbcTemplate into the UserDetailsService bean there.