example directory has some sample code, with a simple user interface.
It's very easy to get CORS errors when doing S3 requests from a web browser. You can't list buckets at all, and you need to set the CORS properties on buckets, with some tool other than a browser, in order to be able to access them from a browser.
s3cmd setcors cors.xml s3://BUCKET
For Amazon S3, you can use the AWS Management Console to set the CORS properties. For Digital Ocean Spaces, you need to do it with an SDK or s3cmd. The Amazon S3 CORS documentation is here.
My thanks to Kevin Tonon for his
elm-aws-core package, and to the-sett for upgrading it to Elm 0.19.1: the-sett/elm-aws-core package. Without it, I would likely have thrown up my hands in despair over ever getting the signing and authorization crypto to work.