Package TWiki::Users::Password 
Base class of all password handlers. Default behaviour is no passwords,
so anyone can be anyone they like.
The methods of this class should be overridded by subclasses that want
to implement other password handling methods.
 ClassMethod new ($session) -> $object 
Constructs a new password handler of this type, referring to $session
for any required TWiki services.
Complete processing after the client's HTTP request has been responded
to. 
-  breaking circular references to allow garbage collection in persistent     environments
 ObjectMethod fetchPass ($login) -> $passwordE 
Implements TWiki::Password
Returns encrypted password if succeeds.  Returns 0 if login is invalid.
Returns undef otherwise.
 ObjectMethod checkPassword ($user,$passwordU) -> $boolean 
Finds if the password is valid for the given login.
Returns 1 on success, undef on failure.
 ObjectMethod deleteUser ($user) -> $boolean 
Delete users entry.
Returns 1 on success, undef on failure.
 ObjectMethod passwd ($user,$newPassU,$oldPassU) -> $boolean 
If the $oldPassU is undef, it will try to add the user, failing
if they are already there.
If the $oldPassU matches matches the login's password, then it will
replace it with $newPassU.
If $oldPassU is not correct and not 1, will return 0.
If $oldPassU is 1, will force the change irrespective of
the existing password, adding the user if necessary.
Otherwise returns 1 on success, undef on failure.
 encrypt( $user, $passwordU, $fresh ) -> $passwordE 
Will return an encrypted password. Repeated calls
to encrypt with the same user/passU will return the same passE.
However if the passU is changed, and subsequently changed 
back
to the old user/passU pair, then the old passE is no longer valid.
If $fresh is true, then a new password not based on any pre-existing
salt will be used. Set this if you are generating a completely
new password.
Return any error raised by the last method call, or undef if the last
method call succeeded.
 ObjectMethod getEmails ($user) -> @emails 
Fetch the email address(es) for the given username. Default behaviour
is to look up the users' personal topic.
 ObjectMethod setEmails ($user,@emails) 
Set the email address(es) for the given username in the user topic.