Does anyone know a cloud service that allows content distribution over SFTP?
Most CDN such as Amazon's S3 or Microsoft's Azure allow me only to use HTTP / HTTPs.
AWS recently added the AWS Transfer for SFTP service that provides you with an SFTP endpoint on top of Amazon S3 so that it scales to infinity and is highly available. The default authentication method that's built in to in the service is key based.
We've recently added a new Heroku add-on, SFTP To Go, based off of that that provides a scalable and robust SFTP as a service solution for Heroku apps, so you can easily distribute content over SFTP with it. The advantages we offer on top of AWS Transfer for SFTP are lower costs (as the endpoint can be shared) and both key and password authentication.