[DOC] Clarify use of handleCustomJob Function

[monkeytronics]

Describe the issue
I am attempting to get an older ESP-IDF V4.3. application up to date. I have pulled the demos. The basic pub/sub examples work nicely. But I am struggling with the OTA.

The V4.3. code used custom jobs in AWS, where we pulled the ota_url and fed it to the http ota updater. We did not use code signing.

I am currently struggling to get the OTA to work here. The example provided is OTA over MQTT. I like this concept as it offers significant saving in terms of memory. So, I would like to use this. I've already set up the IAMs Role and IOT policy for the certificate so the Thing is ready for MQTT jobs and streams.

Would it be possible to provide some guidance on the flow with examples as to how we can get this to work with an unsigned binary. The AWS Console insists on code signing (as far as I can tell) so it's likely we'll need to use the SDK (or CLI as a quick place to test / prove).

Appreciate that this could go into the FreeRTOS forum, but I think it would also be a great addition to the documentation on this repo.

[rawalexe]

Hello @monkeytronics ,
Thank you for your query, I am collecting all the necessary docs and will update you on it soon.

[rawalexe]

If you want to create an OTA update, where the service does not sign the image for the update then you could use custom signed images when creating an OTA Update. See "Using a custom signed firmware image" here: https://docs.aws.amazon.com/freertos/latest/userguide/ota-console-workflow.html

It then falls upon the device agent to disregard the signing information about signing and hashing algorithms and not perform signing verification.
However unsigned binary creates a huge hole security posture and not recommended.

Please, let me know if you have more questions