http-mcp-headers

Implementation guidance for passing secret values through HTTP headers in GitHub Actions MCP configurations. GitHub Actions is a service for running automated workflows, and MCP is a way for an agent to connect to external tools.

In plain words
What is it for?
Use it when configuring an HTTP MCP server whose headers contain GitHub Actions secrets, such as credentials for accessing Datadog dashboards, service-level objectives, or metrics.
Why use it?
It prevents API keys and other secret values from being hard-coded while still making them available to an HTTP-connected service. It also keeps the workflow and connection configuration aligned.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/github/gh-aw/http-mcp-headers
Any agent
npx skills add github/gh-aw --skill http-mcp-headers
Clone the repo
git clone --depth 1 https://github.com/github/gh-aw

Made for: Claude Code, Codex.

Per session 18 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,194 The whole file, excluding the scripts and references it only reads on demand.
Security scan C 1 finding. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00018 $0.01194
Opus 5 $0.00009 $0.00597
Sonnet 5 $0.00004 $0.00239
Haiku 4.5 $0.00002 $0.00119

Measured 2d ago against content hash 537d2fff1660, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade C, and why

http-mcp-headers scanned grade C with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Harvests environment variableshighData exfiltration

Enumerating or grepping the environment for keys collects credentials unrelated to what the mod says it does.

1. Extract secrets from headers (e.g., `${{ secrets.DD_API_KEY }}`)
.github/skills/http-mcp-headers/SKILL.md · 152 lines

How it starts

The opening of the file, as written. The whole thing — 152 lines — stays where its author put it; the contents beside it link to each section on GitHub.

HTTP MCP Header Secret Support - Implementation Summary

Use this reference for HTTP MCP header secret support in the copilot engine.

Problem Statement

When HTTP MCP headers include GitHub Actions secrets, mcp-config.json must:

  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' }}
  COPILOT_GITHUB_TOKEN: ${{ secrets.COPILOT_GITHUB_TOKEN }}
  # ... other env vars

Read the full file on GitHub · 152 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 152 lines · 18 tokens per session scan C 537d2fff1660

Subscribe to this mod's changes

http-mcp-headers is a skill published in the GitHub repository github/gh-aw (5,050 stars, last pushed 2d ago), licensed MIT. It adds 18 tokens to every session and 1,194 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it C with 1 finding (harvests environment variables). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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