Secrets - Microsandbox

Secrets use a placeholder substitution model. The guest VM never sees the real credential.

When you bind a secret to an environment variable and one or more allowed hosts, microsandbox generates a random placeholder (e.g., OPENAI_API_KEY=msb_ph_a8f3c2...) and injects that into the guest instead. The real value never enters the VM. The only way it reaches the outside world is when a request goes to an allowed host, at which point microsandbox swaps the placeholder for the real value. Everywhere else, the placeholder is just a meaningless string.

So even with full code execution inside the sandbox, there's nothing to steal. The credential was never there.

<CodeGroup> ```rust Rust use microsandbox::Sandbox;

let sb = Sandbox::builder("agent") .image("python") .secret(|s| s .env("GITHUB_TOKEN") .value(std::env::var("GITHUB_TOKEN")?) .allow_host("api.github.com") .allow_host_pattern("*.githubusercontent.com") ) .secret_env("OPENAI_API_KEY", api_key, "api.openai.com") .create() .await?;


```typescript TypeScript
import { Sandbox } from "microsandbox";

await using sb = await Sandbox.builder("agent")
    .image("python")
    .secret((s) =>
        s.env("GITHUB_TOKEN")
            .value(process.env.GITHUB_TOKEN!)
            .allowHost("api.github.com")
            .allowHostPattern("*.githubusercontent.com"),
    )
    .secretEnv("OPENAI_API_KEY", process.env.OPENAI_API_KEY!, "api.openai.com")
    .create();

python

import os
from microsandbox import Sandbox, Secret

sb = await Sandbox.create(
    "agent",
    image="python",
    secrets=[
        Secret.env(
            "GITHUB_TOKEN",
            value=os.environ["GITHUB_TOKEN"],
            allow_hosts=["api.github.com"],
            allow_host_patterns=["*.githubusercontent.com"],
        ),
        Secret.env(
            "OPENAI_API_KEY",
            value=os.environ["OPENAI_API_KEY"],
            allow_hosts=["api.openai.com"],
        ),
    ],
)

bash

msb create python --name agent \
  --secret "GITHUB_TOKEN=$GITHUB_TOKEN@api.github.com" \
  --secret "OPENAI_API_KEY=$OPENAI_API_KEY@api.openai.com"

</CodeGroup>

See the SDK Reference for the full API: Rust | TypeScript | Python.