[xwiki-devs] [proposal] Migrate database to store passwords in LargeStringClass and begin using crypto.passwd#protectPassword

Because protectPassword generates a base-64 encoded java serialized form, the size is quite a bit larger than the 255 character limit of StringProperty and thus PasswordProperty. The use of java serialization is central to the upgradability of the password verification function because any new class which implements PasswordVerificationFunction automatically works. Given this, I want to migrate the database to move password hashes into the xwikilargestrings table and change PasswordProperty to extend LargeStringProperty. During this migration, any passwords still stored in plaintext will be ported to the scrypt function, passwords stored as a hash will have an exclamation mark pretended to the text (this is invalid base64) and be inserted into the table as is. PasswordClass will keep the sha-512 hash function for legacy passwords but will port passwords to the new format as users log in. These changes will allow us to close http://jira.xwiki.org/jira/browse/XWIKI-70 and http://jira.xwiki.org/jira/browse/XWIKI-582 WDYT? Caleb