How to save a copy of user's input password?

[Andy]

Hi all,
My pam version is 1.1.0, I use it to authenticate users.
My case is, when pam finished it's auth, that is after
pam_authenticate(pamh, o) & pam_acct_mgmt(pamh, 0),
I want to save a copy of user's password if it's valid, but I can not
find any API to fulfill my needs.
I tried pam_get_item(pamh, PAM_AUTHTOK, (const void
**)&copy_of_passwd), but it returns a "bad item passed to
pam_*_item()", now I have no idea. :(

Please help, thanks.

-Andy