I'm not quite following the problem. You can encode the secret/key using Base32. In fact this Keycloak already stores the secret as a Base32 encoded string. We don't strictly support hardware tokens at the moment as there's no way to specify the secret, but you can probably do that through the admin endpoints.
Yep, I've already done it (via custom realm resources, since there is no SPI for custom *admin* resources yet).
To be accurate: KeyCloak *stores* HOTP secrets as plain strings, but transfers them to phones as Base32. For example:
s7hAVBHOOPvAnTa3w4mh - this is what is stored in the database (plain string)
OM3W QQKW IJEE 6T2Q OZAW 4VDB GN3T I3LI - this is printed out to be entered into FreeOTP / Google Authenticator
When authenticating, the plain string is converted to bytes and used as a secret for HmacOTP. Since storage type is String/VARCHAR, such a secret is limited to printable characters.
My intention was to use the KeyCloak's standard HOTP authenticator to validate OTPs generated by hardware tokens. Unfortunately, tokens that I'm working with (namely Aladdin eToken PASS) are programmed with seeds that contain arbitrary bytes, and therefore they cannot be stored into Credential's "value" field.
But now it turns out that I'll have to implement custom authenticator either way. Thus, I'll just store seeds as hex string and decode them in my authenticator before calling HmacOTP. I'll probably use different credential type, ex., "hotp+", in order not to mess up with KeyCloak OTP.
By the way, do you think having a SPI for credential types could be a good idea (custom/proprietary OTP algorithms; custom storage format, like in my case)? At the moment, all the supported credential types (password, HOTP/TOTP etc.) are hardcoded into org.keycloak.models.utils.CredentialValidation. If we had a SPI, it would become possible to add new types without modifying KeyCloak code - and all the code that uses context.getSession().users().validCredentials(...) could make use of new credential types.
Cheers,
Mitya