[TYPO3-dev] How to use hook on felogin - Disabling login for certain users

[g4-lisz at tonarchiv.ch]

Hi there!

I never used any TYPO3 hooks before...

I would appreciate very much if someone could give me a short step-by-step recipe to achieve the following:

The login for certain frotend users shoud be denied. There should be a lookup in another DB table with a 'login_disabled' flag 
for each user.
I.e. how can I hook a function in the fe login process, which gets the user uid and returns true or false (=allowed or not allowed)?

Cheers,
Till