SignatureError when :Key starts with a slash

[dchelimsky]

> (aws/invoke s3
              {:op      :GetObject
               :request {:Bucket bucket-name
                         :Key    "/path/to/a/file.txt"}})

{:cognitect.anomalies/category :cognitect.anomalies/forbidden
 :Error
 {:Message
  "The request signature we calculated does not match the signature you provided. Check your key and signing method."}}

This is happening because the URI is being generated with a double slash:

> (-> *1 meta :http-request :uri)
"/cognitect-aws-test-1547841641//path/to/a/file.txt"

More context:

The AWS Docs say:

To get an object from such a logical hierarchy, specify the full key name for the object in the GET operation. For a virtual hosted-style request example, if you have the object photos/2006/February/sample.jpg, specify the resource as /photos/2006/February/sample.jpg. For a path-style request example, if you have the object photos/2006/February/sample.jpg in the bucket named examplebucket, specify the resource as /examplebucket/photos/2006/February/sample.jpg

aws-api users don't know (or need to know) whether the client is building a path-style or virtual-hosted-style request, and in either case, the docs indicate that the :Key param should start with a "/". aws-api should ensure that it doesn't produce "//" in the path part of the uri.