Well well. Unfortunately no, but all the parts are around. You have...
...the DBI and the DBD suite of modules for storing your data
... CGI.pm for dealing with cookies, thus, logins
... various validation modules for various bits and pieces of data

There ARE portals out there, which wouldn't be in CPAN. ubb is there, but that's a BBS service more than anything else. There is slashcode, but that may be over doing things a bit. I guess I have to ask.. what is the rest of your site doing? What is the user logging in TO?