How to read this hmackey for arduino?
Those are examples for keys. You need one key and you can choose any text with any length.

Did you see this line in the example:

sha.initHmac((uint8_t*)"Jefe",4);


It uses the key "Jefe" with a length of 4.
You can use your own key, but you also need the length.

char myKey[] = "abece123*";
int length = strlen(myKey);
sha.initHmac((uint8_t*)myKey, length);