This week's book giveaway is in the Agile and other Processes forum. We're giving away four copies of The Mikado Method and have Ola Ellnestam and Daniel Brolund 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.