Webhooks: The Devil in the Details
techblog.commercetools.com
techblog.commercetools.com
I'd also suggest that it would want some form of federation - so instead of external entities pushing directly into your message queue, they'd push to theirs, and your message queue would pull from theirs and push to your consumers. That way, you don't lose messages from your provider when your connection to them fails.
https://www.rabbitmq.com/access-control.html
I am starting to use it at my work but I'm pretty sure I wouldn't open it up to the public, ACLs or not.