Made threading an option for authentication

Done according to the plan outline by Harald by email 

1. In general, i'm happy to remove this parallelization for now and make it an optional command line switch. but in order to make the authentication useful, we have to run it once per connection and per database.

2. please remove these last 2 commits by you (git reset & forced push) ... I can also do this if you like.

3. delete your small pull request

4. add a new pull request to make it non-parallel for testing.

This is 4.