KemalIdentity::Passwords::LegacyVerifier

Verifies a digest produced by the system this application is migrating off.

Why this is verify-only

There is no hash_secret here, and there never will be. A legacy verifier exists so that people can log in with the password they already have; the digest it produces is then immediately replaced by one from the current Hasher. Giving it the ability to write a digest would make it possible to keep creating them, and a migration that can still create rows in the old format is not a migration.

Do not go looking for a library of these

This shard ships the contract and no implementations, deliberately. A ready-made Sha1Verifier would be this project publishing a working SHA-1 password check, and the first thing somebody does with a class that exists is use it for something new. Yours is five lines and looks like this:

class DeviseVerifier < KemalIdentity::Passwords::LegacyVerifier
  def name : String
    "devise"
  end

  def handles?(digest : String) : Bool
    digest.starts_with?("$2a$")
  end

  def verify(secret : KemalIdentity::Secret, digest : String) : Bool
    Crypto::Bcrypt::Password.new(digest).verify(secret.reveal + PEPPER)
  end
end

The rules an implementation has to keep

• Never raise. This runs on the request path against whatever is in the column. A digest written by a system nobody remembers is an expected input, not an error.
• Never truncate. The same rule Hasher states: if the algorithm cuts at n bytes, two different passwords sharing a prefix open the same account.
• Compare in constant time if the comparison is yours to make. Crypto::Subtle.