Optional CA certificates(s): if you have a self-signed CA, you may want to add the CA certificate here, to be able to verify that the server we are connecting to is the real one. If you add it and a man-in-the-middle attack takes place, the link will not be made.

HMAC SHA512 key: it is a string that will be used to sign the payload; this way you can be sure that the server knows the secret and you can go on to process the request. You can use any character you want: letters, digits and any symbol.
The server will create a HMAC over the payload using SHA512 and will add a HTTP header: X-RocketGit-Signature: <signature>. It is recommended to verify it before parsing the body, for security reasons. It is not generated for application/x-www-form-urlencoded encoding.