The authvchkpw module is no longer part of courier-imap /
courier-authlib package. I have rewritten the authvchpw modue and it
is already part of vpopmail release 5.4.27 onwards. You can use it
after usual ./configure and make. copy the authvchkpw module to the
courier-imap's authlib directory and it should work.
The authvchkpw is a bit like checkpassword. i.e. it expects input on
file descriptor 3. The fields are separated by newline. The 5 lines
are