Function sign 

pub fn sign(secret: &str, payload: &str) -> String

HMAC-SHA256 of payload with secret, as lower case hex.

Examples

The test vector 2 of RFC 4231:

use brokapi_bybit_protocol::sign::sign;

assert_eq!(
    sign("Jefe", "what do ya want for nothing?"),
    "5bdcc146bf60754e6a042426089575c75a003f089d2739839dec58b964ec3843"
);