Function import_verifying_key_spki 

pub async fn import_verifying_key_spki(
    variant: RsaVariant,
    salt_length: u32,
    spki: impl Into<Vec<u8>>,
) -> Result<VerifyingKey, Error>

Import a public key as an X.509 SubjectPublicKeyInfo (DER). The declared variant binds the digest at mint, and salt_length — the PSS salt length in bytes — binds there too: the minted key verifies exactly one PSS parameterization, and a signature made under any other salt length fails Error::AuthenticationFailed. Admission follows the RSA family contract (see the WIT rsa interface).