Accept passthrough headers in agent execute

[jiapingzeng]

Description

Create MCP client on each execute request + forward headers to MCP connector

Related Issues

Resolves #[Issue number to be closed when this PR is merged]

Check List

• New functionality includes testing.
• New functionality has been documented.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

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Accepted headers:

- opensearch-url
- aws-region
- aws-access-key-id
- aws-secret-access-key
- aws-session-token
- aws-service-name

Sample request:

POST {{endpoint}}/_plugins/_ml/agents/{{agent_id}}/_execute
--header 'aws-access-key-id: xxx' \
--header 'aws-secret-access-key: xxx' \
--header 'aws-session-token: xxx' \
--header 'opensearch-url: https://xxx.aos.us-east-1.on.aws' \
--header 'aws-region: us-east-1' \
--header 'aws-service-name: es' \

--header 'Content-Type: application/json'
{
    "parameters": {
        "question": "list indices"
    },
    "verbose": "true"
}

Response:

{
    "inference_results": [
        {
            "output": [
                {
                    "name": "memory_id",
                    "result": "F7vALZoBCqjo4z06S5j0"
                },
                {
                    "name": "parent_interaction_id",
                    "result": "GbvALZoBCqjo4z06TZiW"
                },
                {
                    "name": "response",
                    "dataAsMap": {
                        "response": "Here are the indices in your OpenSearch cluster:\n\n## User Indices\n1. **tmdb** - 8,516 documents, green health\n...",
                        "additional_info": {}
                    }
                }
            ]
        }
    ]
}

[Zhangxunmt]

spotless needs to apply

[Hailong-am]

can we change it to x-amzn-datasource-endpoint and add a new header x-amzn-datasource-type

[jiapingzeng]

discussed with team today, we will accept these headers in ml-commons to match opensearch-mcp-server-py

- opensearch-url
- aws-region
- aws-access-key-id
- aws-secret-access-key
- aws-session-token
- aws-service-name