Function grin_core::libtx::aggsig::sign_single

pub fn sign_single(
    secp: &Secp256k1, 
    msg: &Message, 
    skey: &SecretKey, 
    snonce: Option<&SecretKey>, 
    pubkey_sum: Option<&PublicKey>
) -> Result<Signature, Error>

Just a simple sig, creates its own nonce if not provided