[Serusers] Check_from()

[Greg Fausak]

I've run into a problem (again) where I'm worried about the registration
and invite identity.  I've got the appropriate check_from() which
verifies
that the from uri contains a user in the subscriber table.  

The README in uri :
-------
1.4.3. check_from()

   Check From username against URI table or digest credentials.
--------
I can't tell from the description if this means that *any* user
will work?  Can the user in the from() field be different that the
user in the digest credentials?  How can I be sure that the from
matches the credentials?

---greg