S3-backed content addressable storage. Store files by their sha256 sum. Automatically compresses it in S3 if it's compressible.
var CAS =var cas = options
bucket- s3 bucket name
key- s3 key
secret- s3 secret key
cdn- optional CDN host, defaulting to the s3 bucket, such as
Get an S3 key from a string or a buffer and an extension.
var key = await cas
Get a URL for the key, depending on whether you'd like to use the S3 bucket directly or a CDN.