Credentials

Most agents need an API key for their model provider. An HTTP/HTTPS proxy on your host intercepts outbound requests from the sandbox, looks up the matching credential on the host, and overwrites the auth header before forwarding. The real credential stays on the host; the sandbox sees only a sentinel value. For the security model behind this, see Credential isolation.

How credential injection works

When a sandbox makes an outbound request, the host-side proxy decides three things: whether the request matches a service the kit (or built-in agent) declares, what header to write, and what value to inject. The kit declares the match and the header; you provide the value on the host. The real value never enters the sandbox — the agent sees only a sentinel like proxy-managed.

There are several ways to provide that value. When more than one source has a value for the same service, the stored secret takes precedence over a host environment variable.

For multi-provider agents (OpenCode, Docker Agent), the proxy selects credentials based on the API endpoint being called. See individual agent pages for provider-specific details.

Stored secrets

sbx secret set stores credentials in your OS keychain, keyed on a service identifier. Built-in agents declare a fixed set of services. Custom kits can declare their own. The same sbx secret set flow works for both.

Where secrets are stored

The store backing sbx secret set depends on your operating system:

• macOS: the system Keychain.
• Windows: the Windows Credential Manager.
• Linux: the Secret Service exposed by your desktop keyring, such as GNOME Keyring or KDE Wallet.

The Ubuntu package depends on GNOME Keyring, so a standard desktop install needs no extra setup.

On Linux hosts without a running Secret Service — headless servers and some WSL setups — sbx falls back to an encrypted file under your user config directory $XDG_CONFIG_HOME/com.docker.sandboxes, which defaults to ~/.config/com.docker.sandboxes when $XDG_CONFIG_HOME is unset. The fallback is automatic and needs no configuration. When you store a secret this way, sbx prints a notice:

No keychain detected - this secret will be stored in an encrypted file on disk

The file is encrypted at rest and protected by 0700 directory permissions, the same posture as ~/.docker/config.json. This is weaker than an OS keychain, which also mediates access per application. If you start a Secret Service on the host later, sbx stores new secrets in the keychain again. For more on running sandboxes without a desktop keyring, see Can I use Docker Sandboxes on headless Linux?

Store a secret

$ sbx secret set -g anthropic

This prompts you for the secret value interactively. The -g flag stores the secret globally so it's available to all sandboxes. To scope a secret to a specific sandbox instead:

$ sbx secret set my-sandbox openai

Note

A sandbox-scoped secret takes effect immediately, even if the sandbox is running. A global secret (-g) only applies when a sandbox is created. If you set or change a global secret while a sandbox is running, recreate the sandbox for the new value to take effect.

You can also pipe in a value for non-interactive use:

$ echo "$ANTHROPIC_API_KEY" | sbx secret set -g anthropic

Built-in services

Each built-in service name maps to a set of environment variables the proxy checks and the API domains it authenticates requests to:

When you store a secret with sbx secret set -g <service>, the proxy uses it the same way it would use the corresponding environment variable. You don't need to set both.

Services declared by kits

Custom kits can declare their own service identifiers in spec.yaml — they're not limited to the table above. To provide a credential for a kit-declared service, run sbx secret set with the same identifier the kit declares under credentials.sources:

$ sbx secret set -g my-service

There's no separate registration step; the keychain entry is keyed on the identifier the kit already uses. See Authenticate to external services for the kit-side wiring.

List and remove secrets

List all stored secrets:

$ sbx secret ls
SCOPE      TYPE      NAME      SECRET
(global)   service   github    gho_GCaw4o****...****43qy

Remove a secret:

$ sbx secret rm -g github

Note

Running sbx reset deletes all stored secrets along with all sandbox state. You'll need to re-add your secrets after a reset.

GitHub token

The github service gives the agent access to the gh CLI inside the sandbox. Pass your existing GitHub CLI token:

$ echo "$(gh auth token)" | sbx secret set -g github

This is useful for agents that create pull requests, open issues, or interact with GitHub APIs on your behalf.

SSH agent

If your host has an SSH agent and SSH_AUTH_SOCK is set, Docker Sandboxes forwards the agent into the sandbox and sets SSH_AUTH_SOCK there. The private keys stay on your host. Processes inside the sandbox can request signatures from the forwarded agent, but they can't read or copy the private key.

Use SSH agent forwarding for Git operations over SSH and SSH-based commit signing. The signing key must be loaded in the host SSH agent for sandboxed commit signing to work. Outbound SSH connections are still subject to sandbox network policy. For details, see Commit signing.

Custom secrets

Important

Custom secrets are experimental. Behavior, flags, and the placeholder format may change without notice.

For credentials that don't fit the service-identifier model — for example, when an agent validates the environment variable format at boot, or when the credential lands in a request body rather than a header — use sbx secret set-custom. The secret is keyed on one or more target domains, an environment variable name, and an optional placeholder string, instead of a service identifier.

$ sbx secret set-custom -g \
    --host api.example.com \
    --env API_KEY \
    --value <secret>

Repeat --host to cover multiple domains with the same secret — useful when an API is split across related hostnames or when two unrelated endpoints share a credential:

$ sbx secret set-custom -g \
    --host api.example.com \
    --host uploads.example.com \
    --env API_KEY \
    --value <secret>

A --host value can also use wildcards, with the same syntax as network rules: * matches a single label (*.example.com covers api.example.com) and ** matches any number (**.example.com covers api.example.com and v2.api.example.com).

Warning

Passing the secret as --value <secret> records it in your shell history and exposes it to other processes running as your user. Avoid pasting real credentials inline — read the value from a variable that's already in your environment, and clear shell history if a real secret was passed on the command line.

Inside the sandbox, API_KEY is set to a generated placeholder (for example, sbx-cs-<rand>). When a sandboxed process sends a request to any of the configured hosts and the placeholder appears anywhere in the request, the proxy replaces it with the real value. The agent never sees the real secret.

Prefer the service-based flow whenever it's an option — the kit handles the wiring; you only provide the value.

Environment variables

As an alternative to stored secrets, export the relevant environment variable in your shell before running a sandbox:

$ export ANTHROPIC_API_KEY=sk-ant-api03-xxxxx
$ sbx run claude

The proxy reads the variable from your terminal session. See individual agent pages for the variable names each agent expects.

Note

These environment variables are set on your host, not inside the sandbox. Sandbox agents are pre-configured to use credentials managed by the host-side proxy. For custom environment variables not tied to a built-in service, see Setting custom environment variables.

Registry credentials

Registry credentials authenticate to private OCI registries when pulling templates or kits, and can also let the agent pull and push images from inside the sandbox. Use sbx secret set --registry <host> to store them. For Docker Hub, sbx reuses your sbx login session — no registry secret needed. For other registries (GitHub Container Registry, ECR, ACR, self-hosted Nexus, and so on), store credentials with sbx secret set --registry.

The scope you store a credential at controls where it's used — and whether its value enters the sandbox. The scope comes from how you target sbx secret set:

sbx secret set [-g | SANDBOX] --registry HOST

• Host-only (no -g, no SANDBOX): the sbx CLI uses it to pull templates and kits when creating a sandbox. The credential stays on the host and is never available inside the sandbox.
• Global (-g): same as host-only, plus written into ~/.docker/config.json in every new sandbox so the agent can pull and push images. The value lives inside the VM, where the agent can read it, so it's less isolated than the proxy-injected service credentials above. Use it when agents build and publish container images.
• Sandbox-scoped (SANDBOX): same in-sandbox behavior as global, but only for the named sandbox. Use it when only one sandbox needs registry access.

Note

Registry credentials are written into a sandbox at creation time. Recreate an existing sandbox to pick up credentials added after it was created.

Store registry credentials

Pipe a token from stdin and target the registry hostname:

$ gh auth token | sbx secret set --registry ghcr.io --password-stdin

For registries that require a username (for example, ACR with an admin account), add --username:

$ echo "$ACR_PASSWORD" | sbx secret set \
    --registry myregistry.azurecr.io \
    --username myuser \
    --password-stdin

Add -g to store the credential globally, before you create the sandbox:

$ gh auth token | sbx secret set -g --registry ghcr.io --password-stdin
$ sbx run claude                      # created with the credential in place

To scope the credential to a single sandbox, store it under that sandbox's name and create the sandbox with the same name:

$ gh auth token | sbx secret set my-app --registry ghcr.io --password-stdin
$ sbx run claude --name my-app

sbx kit pull also uses these credentials, with the Docker credential store as a fallback. sbx kit push uses only the Docker credential store — push targets still require a prior docker login.

Remove registry credentials

Remove both the host-only and global entries for a registry:

$ sbx secret rm --registry ghcr.io -f

To remove only the global (in-sandbox) entry and leave the host-only credential in place, pass -g:

$ sbx secret rm -g --registry ghcr.io -f

To remove a sandbox-scoped credential, pass the sandbox name:

$ sbx secret rm my-sandbox --registry ghcr.io -f

Best practices

• Use stored secrets over environment variables. Stored secrets are encrypted at rest in the OS keychain (or an encrypted file on Linux hosts without a keychain), while environment variables are plaintext in your shell. See Where secrets are stored.
• Don't set API keys manually inside the sandbox. Sandbox agents are pre-configured to use proxy-managed credentials.
• Registry credentials you make available inside a sandbox are stored in the VM (~/.docker/config.json), where the agent can read them — unlike proxy-injected service credentials, which never enter the sandbox. Reserve them for sandboxes that need registry access, and prefer sandbox scope over global (-g) to limit exposure.
• For Claude Code and Codex, OAuth is another secure option: the flow runs on the host, so the token is never exposed inside the sandbox. If you haven't stored a credential, both agents prompt you to authenticate before the sandbox launches — Codex prompts on the host from sbx run codex, and Claude Code prompts inside the agent. To authenticate ahead of time, run sbx secret set -g openai --oauth for Codex, or use /login inside Claude Code.
• If you store credentials in 1Password, see Sourcing credentials from 1Password for how to use op read and op run with sbx.

Custom templates and placeholder values

When building custom templates or installing agents manually in a shell sandbox, some agents require environment variables like OPENAI_API_KEY to be set before they start. Set these to placeholder values (e.g. proxy-managed) if needed. The proxy injects actual credentials regardless of the environment variable value.