[asterisk-users] control during registration process

[unplug]

Hi all,
  As we know, we can use dial plan to control the flow of the call
making process.  However, I want to know how to control during the
registration process.  Say, in ARA, during the registration process,
there is update sql statement in the user table.  And I want to store
more information in the table such as uri.   Where can I control
asterisk to make the change in registration process?