[sork] how to config default/prefer password backend ?

[Adrian Mak]

I install horde - passwd 3.0
It'll will be used for email users to change their email password thru web.
Therefore, I configured passwd not to provide an password backend list and I
configured to use sql as the backend to change the password.

My question is how to by default use the sql as the backend when submitting
the change password form ?