[davedx]

Wait wait. Why would you truncate it after input unless... you're storing it in plaintext?

[orblivion]

Maybe the KDF gets really slow with a super long input.

[zja]

You truncate passwords to prevent DOS

[lesuorac]

Why not either show an error or do a client-side hash so there's a fixed length?

[orblivion]

Showing an error is probably the right thing. Client-side mitigations wouldn't prevent a DOS.