MCP secrets

A clever way to pass in secrets to MCPs

I’ve been on a quest to learn everything about MCPs and OAuth, especially Dynamic Client Registration. The journey and details there are worth a post of their own, which I’ll write in the future (a quick tease, check out this repository with my research so far: https://github.com/thiagorobert/FastMCPv2-example)

Right now I really just want to point out superargs. It solves a problem I’ve been grappling with since I embarked on this journey. The MCP I wrote is a proxy to Github’s API, and it requires a secret (auth token or Personal Access Token) to access Github data. I ended up creating an OAuth App in my Github account, and wrote some code to perform OAuth using that app and save the token to a file, which I can then feed to my MCP using .env or environment variables.

But that’s incredibly lame, right? I want my MCP to work for everyone. Ideally, I would like to host it somewhere (Fargate?) and would like folks to be able to use it to access their own repositories, using their own secrets as needed. I spent A LOT of time trying to figure out a way to do that. Today I attempted to implement OAuth Token Exchange (rfc8693) to solve that problem without success (I believe Github simply doesn’t support it). I also learned that Github Enterprise lets you create enterprise-level Personal Access Tokens and OAuth Apps, which would allow my MCP to retrieve data for all repositories within that enterprise.

I was pretty much resigned to just live with this limitation, when I found https://supermachine.ai, a service that lets you quickly deploy your own MCPs (note to self, I also want to explore https://gofastmcp.com/deployment/fastmcp-cloud). I started looking into code by Supercorp, the entity behind that service, when I found superargs.

In a nutshell, superargs wraps your MCP around a different MCP which provides a new tool ‘Update args’. So, during a conversation with an LLM, you can just say “list available repositories using githubToken <your token here>”. The LLM knows to call that tool to update the argument for the wrapped MCP, and use the now functional wrapped MCP to list repositories you have access to given your credentials. If this sounds confusing, it’s because it is. I wouldn’t be able to make sense of this if I had not spent quite a few hours mulling this problem.

Here’s my Claude Desktop (which I’m running on Linux) demonstrating the use of superargs and another of their tools, supergateway:

{
  "mcpServers": {
    "supermachineHost": {
      "command": "npx",
      "args": [
        "-y",
        "supergateway",
        "--sse",
        "https://mcp-server-728d3008-180f-4c91-9c28-74624ae7f1b5.supermachine.app"
      ]
    },
    "mygithub": {
      "command": "npx",
      "args": [
        "-y",
        "superargs",
        "--stdio",
        "GITHUB_ACCESS_TOKEN= uv --directory /workspace/github/FastMCPv2-example run mcp_server.py"
      ]
    }
  }
}

supergateway is pretty cool too - it also solves a problem I’ve dealt with during my MCP exploration journey. But the details are probably fodder for a future post. Both of these tools feel a bit hacky at first glance, but all of this tech is so bleeding edge that you have to think outside of the box to get things working - I like that mindset. Also, folks at Supercorp are literally building a business backed by that code, so props to them!