The secret used for authenticating the webhooks. When we send webhooks to your endpoint, we will add a truepic-signature header to those requests that we generate using this secret. When your endpoint receives a webhook POST request, you can then verify that the request was signed with this secret to ensure that the request is from us. If you want to remove the secret, set this to null. If you want to set a new secret, provide the new secret string. If you don't want to change the secret, omit this field.