Function decode_secret_hex 

pub fn decode_secret_hex(
    value: &str,
) -> Result<Zeroizing<Vec<u8>>, FromHexError>

Decode hex that holds a secret, such as the commit-log signer, straight into a zeroizing buffer. hex::decode would leave a partly decoded secret in its own buffer on an error. A 0x or 0X prefix is accepted, as hex::decode does.