Encode with JWT Signing Secret
Journey Builder uses the JWT Signing Secret from the package containing the activity as the default signing key for the JWT.
"useJwt": true in the activity's arguments for each call (save, validate, publish, execute) for which you wish to receive a JWT. If you don't include a
customerKey, Journey Builder uses the JWT Signing Secret to verify the JWT.
If you are using the External Key as the signing key, then
customerKey is required.