Add DataPlaneTokenSource and EndpointTokenSource

[emmyzhou-db]

What changes are proposed in this pull request?

Direct Dataplane Access for Databricks Java SDK

This PR adds the required classes for direct dataplane access in the Databricks Java SDK.

DataPlaneTokenSource

• Manages and caches EndpointTokenSource instances.
• Ensures a single EndpointTokenSource per unique endpoint and set of authorization details.
• Provides a thread-safe cache to avoid redundant token source creation.

EndpointTokenSource

• Handles the OAuth token exchange process.
• Exchanges a control plane token for a dataplane token.
• Caches the dataplane token and manages its refresh and expiry.

TokenEndpointClient

• Utility for making HTTP requests to OAuth token endpoints.
• Handles request formatting, response parsing, and error handling.

How is this tested?

• Unit tests have been added for all the aforementioned classes.

NO_CHANGELOG=true

[emmyzhou-db]

Since we’re using objects of this class as HashMap keys, we need to override the equals() method to define when two keys are considered equal, and the hashCode() method so the HashMap can efficiently store and retrieve the values by keys.

[parthban-db]

One thing that we can test more in dataplaneTokenSource is whether we are using the cached endpointTokenSource or not for the same key (the number of times we are calling the endpointTokenSource constructor). It may not need to be fit on the same parameterized tests as this is a different kind of test.

Rest is LGTM!

[parthban-db]

Also, can you change the PR title to something more relevant to the change, like "Add DataPlaneTokenSource?"

[github-actions]

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Trigger:
go/deco-tests-run/sdk-java

Inputs:

• PR number: 449
• Commit SHA: ba40e9492b6d5f07fd20b0692656477d463279fc

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