Generating users accounts inside Google App Engine
If you don't want to require a Google Account or OpenID account you have to roll your own accounts system. This gives you maximum freedom, but it is a lot of work and makes you responsible for password security (ouch). Personally I would advise you to reconsider this requirement -- OpenID especially has a lot going for it (except IIUC it's not so simple to use Facebook).
For a project, I'm going to create an application on Google App Engine where:

Discussion Leaders can register with their e-mail address (or OpenID or Google Account) on the website itself to use it. 
In the application admin page they can create a group discussion for which they can add users based on their e-mail address 
and these users should then receive generated account details (if they don't have accounts yet) making them able to log in to that group discussion with their newly created account.

I don't want to require discussion leaders to having a Google Account or OpenID account in order to register for the application and all user other accounts must be generated by the discussion leader.
However Google App Engine seems to only support Google Accounts and OpenID accounts. How would I go about this? Is there an existing pattern for creating leader-accounts and generating user-accounts from within the Google App Engine which still support the GAE User API?