Drop support for vended OAuth2 tokens (aka "table sessions")

[adutra]

It is in theory possible for a catalog server to "vend" an OAuth2 token to the REST client. This creates a so-called "table session", where the vended OAuth2 token will be used by all FileIO instances created for that table.

But, this is against OAuth2 principles.

Besides, it makes caching of sessions a lot more complex.

And finally, the two open-source REST catalogs that server as reference implementations today, Apache Polaris and Nessie, do not use this feature and do not plan to use them.

Note: this won't hinder any of the ideas outlined in #132.

[dimas-b]

Does this "vending" mean that the Catalog server provides an OAuth2 token, which it in turn obtained from some external IdP?

[adutra]

Yes. To my best knowledge only Tabular used to do this.