In Eclipse Jetty, the Digest authentication server-side component uses ISO-8859-1 to encode the password as bytes.



This was done because the initial specification for HTTP did not specify explicitly a charset, and it was assumed to be ISO-8859-1 for historical reasons.



If the password contains characters that cannot be represented in ISO-8859-1, they are silently replaced by `?`. This happens with passwords that contain Chinese, Cyrillic or Greek characters, for example: `αβ123` converts to `??123`.



An attacker can send a request with a digest `Authorization` header crafted with a password made of only `?` characters; the server would match any password of the same length that contains non-ISO-8859-1 characters.



Recent HTTP Digest [RFC-7616](https://datatracker.ietf.org/doc/html/rfc7616) supports a `charset` parameters that defaults to UTF-8 that allows for correct encoding/decoding of passwords.