Client Bucket Authentication: Get a bucket JWT from the Hub and use it to access the R2 bucket

[jstlaurent]

Context

Once the Hub's token endpoint has been updated, the client will be able to obtain a bucket JWT to perform upload or download operations on the bucket.

Description

Update the way the client interacts with the R2 bucket:

• Prior to performing an operation (or a series of related operations in the case of a Zarr archive), obtain a bucket JWT from the Hub.
• Use a dedicated S3 client to connect to the bucket, instead of the Polaris fsspec implementation
• Use the bucket JWT when authenticating with the S3 client

Acceptance Criteria

• The client does not use the Polaris fsspec implementation when interacting with the R2 bucket

Links

• Polaris Client Authentication Design Document
• Hub token endpoint issue