Base64ByteStringConverter

String ↔ okio.ByteString via Base64 (RFC 4648).

Same type pair as StringByteStringConverter (UTF-8), so it is an alternate: auto-discovery resolves one converter per type pair. Select this one either per-field with @ConvertWith(Base64ByteStringConverter::class), or register it in your @KMapperConfig(converters = [...]) instead of the UTF-8 converter.

Decoding accepts both the standard and URL-safe alphabets and rejects malformed input with IllegalArgumentException. Encoding uses the standard alphabet with padding.