[sda-download] Returns ListAllMyBucketsResult when user does not have access to a dataset

[KarlG-nbis]

Describe the bug

If a user does not have access to a dataset when using the "/s3" paths sda-download returns a ListAllMyBucketsResult(ListBuckets) response containing all datasets the user has access to as buckets.

Steps to reproduce

curl -H "Authorization: Bearer $token" https://download.bp.nbis.se/s3/not_dataset_exists/file_no.exists 

=>

<?xml version="1.0" encoding="UTF-8"?>
<ListAllMyBucketsResult><Buckets></Buckets><Owner></Owner></ListAllMyBucketsResult>

(The given token used in example does not have access to any datasets)

Expected behavior

• If a user attempts to download a file which he does not have access to, or which do not exists, a 403 error code should be returned (not exposing information if file was found or user lacks permissions, to reduce amount of information exposed)
• Tests verifying the fix are added

Additional context

Cause parseParams only populate the "dataset" param in the gin context if requested path starts with a dataset the user has access to, meaning if user does not have access to the requested dataset in the path, the ListBuckets func is called

Estimation of size

small

Estimation of priority

medium