Idea: typo-resistant password check

What if a user can make a typo in password...

1. If server stores password in plaintext, let it just compute Levenshtein distance between valid password and entered.

2. If it must/should store password in form of hash(es) (which is more secure, of course),
let it store all possible passwords with typos where L. distance is ~1-2.
(Not very big list.)