Remove identity-related feature flagged code from the RestController

[cwperks]

Description

This PR is a follow-up to #14630. This PR removes code in the RestController that was behind the opensearch.experimental.feature.identity.enabled feature flag.

The problem with the current code behind the feature flag is that it uses the RestTokenExtractor which assumes that authinfo is provided on the AUTHORIZATION header and is not directly usable by the security plugin in the current state. This PR removes the code to leave it up to the Identity plugin how to provide the subject information. For instance, this PR updates the identity-shiro plugin to utilize ActionPlugin.getRestHandlerWrapper to authenticate a web request and hydrate information about the current subject. The RestTokenExtractor has been moved into the identity-shiro plugin which only supports basic auth with the AUTHORIZATION header in its current state.

I'm opening this PR as a step towards removing the Identity feature flag (but keeping the interface marked as experimental).

I am planning to ask plugin maintainers to remove usages of ThreadContext.stashContext after the experimental feature flag for identity is removed.

Related Issues

Related to opensearch-project/security#4439

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
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[github-actions]

❌ Gradle check result for e6b82ba: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for bc610a2: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❕ Gradle check result for 1abfe97: UNSTABLE

• TEST FAILURES:

      2 org.opensearch.cluster.MinimumClusterManagerNodesIT.testThreeNodesNoClusterManagerBlock
      1 org.opensearch.remotestore.RemoteStoreStatsIT.testNonZeroPrimaryStatsOnNewlyCreatedIndexWithZeroDocs

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[github-actions]

❌ Gradle check result for 34bc922: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for 34bc922: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for 34bc922: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for c2d9a3a: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for c2d9a3a: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

✅ Gradle check result for c2d9a3a: SUCCESS

[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/OpenSearch/backport-2.x 2.x
# Navigate to the new working tree
pushd ../.worktrees/OpenSearch/backport-2.x
# Create a new branch
git switch --create backport/backport-15430-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 1bc81d3eee07e96b6c6393510b41d194276e204c
# Push it to GitHub
git push --set-upstream origin backport/backport-15430-to-2.x
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/OpenSearch/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-15430-to-2.x.

[reta]

@cwperks could you please backport to 2.x manually? thank you!

[cwperks]

@reta opened a manual backport that resolves conflicts in the CHANGELOG: #16004