Webhooks helps you to trigger some actions on your server when an event happens with you repositories.

Key: a string used to "sign" the requests to your server. You can create it using any character you want: letters, digits and any symbol.
The server will create a HMAC over the payload using SHA512 and will add 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 type.