HTTP MCP Header Secret Support - Implementation Summary

This document demonstrates the complete implementation of HTTP MCP header secret support for the copilot engine.

Problem Statement

When using HTTP MCP tools with headers containing GitHub Actions secrets, the generated mcp-config.json needs to:

1. Extract secrets from headers (e.g., ${{ secrets.DD_API_KEY }})
2. Declare those env variables in the execution step
3. Configure the MCP config's "env" section to passthrough those variables
4. Use the passed variables in the headers section

Example Workflow

on:
  workflow_dispatch:
permissions:
  contents: read
engine: copilot
mcp-servers:
  datadog:
    type: http
    url: "https://mcp.datadoghq.com/api/unstable/mcp-server/mcp"
    headers:
      DD_API_KEY: "${{ secrets.DD_API_KEY }}"
      DD_APPLICATION_KEY: "${{ secrets.DD_APPLICATION_KEY }}"
      DD_SITE: "${{ secrets.DD_SITE || 'datadoghq.com' }}"
    allowed:
      - search_datadog_dashboards
      - search_datadog_slos
      - search_datadog_metrics
      - get_datadog_metric

# Datadog Dashboard Search

Search for Datadog dashboards and provide a summary.

Generated Output

1. MCP Config (mcp-config.json)

{
  "mcpServers": {
    "datadog": {
      "type": "http",
      "url": "https://mcp.datadoghq.com/api/unstable/mcp-server/mcp",
      "headers": {
        "DD_API_KEY": "${DD_API_KEY}",
        "DD_APPLICATION_KEY": "${DD_APPLICATION_KEY}",
        "DD_SITE": "${DD_SITE}"
      },
      "tools": [
        "search_datadog_dashboards",
        "search_datadog_slos",
        "search_datadog_metrics",
        "get_datadog_metric"
      ],
      "env": {
        "DD_API_KEY": "\\${DD_API_KEY}",
        "DD_APPLICATION_KEY": "\\${DD_APPLICATION_KEY}",
        "DD_SITE": "\\${DD_SITE}"
      }
    }
  }
}

2. Execution Step Environment Variables

env:
  DD_API_KEY: ${{ secrets.DD_API_KEY }}
  DD_APPLICATION_KEY: ${{ secrets.DD_APPLICATION_KEY }}
  DD_SITE: ${{ secrets.DD_SITE || 'datadoghq.com' }}
  GH_AW_MCP_CONFIG: /home/runner/.copilot/mcp-config.json
  COPILOT_GITHUB_TOKEN: ${{ secrets.COPILOT_GITHUB_TOKEN }}
  # ... other env vars

Implementation Details

Key Functions

1. extractSecretsFromValue(value string) - Extracts secret expressions from a string - Parses ${{ secrets.VAR_NAME }} patterns - Handles default values: ${{ secrets.VAR || 'default' }} - Returns map of variable names to full expressions

2. extractSecretsFromHeaders(headers map[string]string) - Extracts all secrets from HTTP headers - Iterates through all header values - Collects all unique secret expressions - Returns consolidated map of secrets

3. replaceSecretsWithEnvVars(value string, secrets map[string]string) - Replaces secret expressions with env var references - Transforms ${{ secrets.DD_API_KEY }} to ${DD_API_KEY} - Used in MCP config headers rendering

4. collectHTTPMCPHeaderSecrets(tools map[string]any) - Collects secrets from all HTTP MCP tools - Scans all tools for HTTP MCP configurations - Extracts secrets from each tool's headers - Returns consolidated map for execution step env

Rendering Logic

In renderSharedMCPConfig (mcp-config.go):

1. Extract secrets when rendering HTTP MCP configs for copilot engine
2. Add env section to property order when secrets are found
3. Render headers with env var references instead of secret expressions
4. Render env with passthrough syntax (\${VAR_NAME})

In GetExecutionSteps (copilot_engine.go):

1. Collect all HTTP MCP header secrets from workflow tools
2. Add to execution step env map with secret expressions

Security Benefits

1. Secrets never appear in MCP config - Only env var references
2. Proper GitHub Actions secret handling - Uses ${{ secrets.* }} syntax
3. Environment isolation - Each MCP server receives only its required secrets
4. Consistent pattern - Matches existing GitHub remote MCP server implementation

Test Coverage

Unit Tests (mcp_http_headers_test.go)

• extractSecretsFromValue
• extractSecretsFromHeaders
• replaceSecretsWithEnvVars
• collectHTTPMCPHeaderSecrets
• renderSharedMCPConfig with HTTP headers

Integration Tests (copilot_mcp_http_integration_test.go)

• Single HTTP MCP tool with secrets
• Multiple HTTP MCP tools
• HTTP MCP without secrets
• Property ordering
• Env variable sorting

All tests pass ✓