[Extensions] Generate auth tokens for service accounts

[stephen-crawford]

Description

This is a PR to introduce the functionality for generating an auth token for an extension. The auth token consists of a an encoded basic auth token created from a randomly generated password. The token is then passed back to the client so that changes can be made in core in order to later perform authentication and authorization using the token.

Issues Resolved

This issue addresses This PR covers issue #2611 and issue #2668.

Testing

New tests are added to the UserApiTest file.

Check List

• New functionality includes testing
• New functionality has been documented
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[DarshitChanpura]

Request 1 change. Looks good to me otherwise.

[DarshitChanpura]

orElseThrow will not be utilized here as the value will either be a boolean or it will throw an NPE stating return value of isEnabled is null. In order to utilize orElseThrow to catch a missing isEnabled or isService property in SecurityJsonNode, you can make following changes:

        UserServiceException e = new UserServiceException(AUTH_TOKEN_GENERATION_MESSAGE);
        boolean isService = readBooleanFromJsonNode(securityJsonNode, "isService", e);
        boolean isEnabled = readBooleanFromJsonNode(securityJsonNode, "isEnabled", e);
        
        if(!isService || !isEnabled) {
            throw e;
        }

        private boolean readBooleanFromJsonNode(SecurityJsonNode node, String key, Exception e) {
	    return Boolean.parseBoolean(Optional.ofNullable(node.get(key)).orElseThrow(() -> e).asText());
	}

[DarshitChanpura]

LGTM. Thanks @scrawfor99 !

[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-2.x 2.x
# Navigate to the new working tree
cd .worktrees/backport-2.x
# Create a new branch
git switch --create backport/backport-2716-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 1201335bd1c95fc2bb7e9b2210ffe5e029457d25
# Push it to GitHub
git push --set-upstream origin backport/backport-2716-to-2.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-2716-to-2.x.