See TWiki:Support/TWikiRegistrationHowToCheckUsername and TWiki:Support/PreventReRegistration as examples of the need.

I suggest the following user hooks:

1. Two hooks in the form processing. To Check the values in the form both berfore and after the current validation of required fields. There are some cases where a specific registration might need a check more complex than merely required fields.

Example

My own site makes use of professional certification. If the registrant has a certification (check box) then the certifcation number should be supplied as well. The certification number should be unique (i.e. not used by anyone else) and should be a number. It cannot be a required field because there are a number of possible certifications. Only one is required but it could be any one of a number of them.

1. A hook in the verification code processing.

Example

My own site makes use of professional certification. Depending on which check-box are marked the newly verified user will needed to be added to one or more of a number of groups.

-- AA

http://twiki.org/cgi-bin/view/Codev/RegisterCgiScriptRewrite details my thoughts on this. The code used to have the facility to call out during registration for the data to be augmented. But I think I noticed that this feature was deleted a while back. I'd be happy to show you where in the code you'd need to make changes.

-- MC

Undeferred, post Dakar CC