opencode-anthropic-console

An opt-in companion plugin for @ex-machina/opencode-anthropic-auth. It fills in the Claude Code client-attestation transforms for the subset of sk-ant-api03-... keys that require them — typically Anthropic Enterprise / Claude-Code-scoped keys.

Both of @ex-machina/opencode-anthropic-auth's API-key-oriented login flows — "Create an API Key" (which OAuths into Console and exchanges for an sk-ant-... key) and "Manually enter API Key" (paste-in) — end up with the credential stored as auth.type === 'api', and @ex-machina/opencode-anthropic-auth's request-time loader is a no-op on that branch. For regular Console keys that's fine; for attestation-strict keys every request silently fails with 429 rate_limit_error: "Error".

This plugin is not a replacement for @ex-machina/opencode-anthropic-auth. Install it alongside only if you need it.

Do I need this?

You need this plugin only if all of the following are true:

1. Your opencode Anthropic credential is an API key — either via @ex-machina/opencode-anthropic-auth's "Create an API Key" flow (OAuth into Console, exchange for an sk-ant-... key) or its "Manually enter API Key" option (paste-in). Both end up stored as auth.type === 'api'. (Pro/Max OAuth is unaffected — @ex-machina/opencode-anthropic-auth handles that itself.)
2. Your requests come back with 429 rate_limit_error: "Error" (the literal word "Error", not a real rate-limit message).

That error is Anthropic's server-side attestation rejection. It's the signal that your key is Claude-Code-scoped / Enterprise-scoped and enforces strict client fingerprinting. In that case, install this plugin alongside @ex-machina/opencode-anthropic-auth.

If your API key already works without this plugin (most regular Console keys do), you don't need it. Skip it.

Why @ex-machina/opencode-anthropic-auth alone isn't enough for attested keys

@ex-machina/opencode-anthropic-auth's loader gates every transform on auth.type === 'oauth'. That's true only for Claude Pro/Max — the one flow where opencode stores an OAuth access/refresh token pair as the credential.

Its two API-key flows are different:

• "Create an API Key" runs an OAuth handshake against Console and then immediately exchanges the access token for a long-lived sk-ant-api03-... key. The exchanged key is what gets stored. At request time, auth.type === 'api'.
• "Manually enter API Key" stores the pasted key directly. At request time, auth.type === 'api'.

In both cases the loader falls through to return {} — no transforms, no header spoofing, no system-prompt rewrite, no ?beta=true, no tool-name prefixing. This is by design: for regular Console keys there's no attestation to satisfy. For Enterprise / Claude-Code-scoped keys, though, it leaves every request un-fingerprinted, and Anthropic's server rejects them.

This plugin activates only on auth.type === 'api' and applies the missing pipeline, leaving Pro/Max OAuth completely untouched.

Scope / matrix

| Login flow | Stored auth.type | @ex-machina/opencode-anthropic-auth | This plugin | |---|---|---|---| | Claude Pro/Max | oauth | full transforms | skipped (return {}) | | Create an API Key | api | passthrough, no transforms | full transforms | | Manually enter API Key | api | passthrough, no transforms | full transforms |

Because each plugin activates on a distinct auth.type, they never collide at the request level.

Why not just open a PR to @ex-machina/opencode-anthropic-auth?

Fair question. The short answer is that this plugin's behavior is incompatible with the upstream's design contract for its auth.type === 'api' branch (which covers both the "Create an API Key" and "Manually enter API Key" flows), so merging upstream would regress every existing user of those flows.

The concrete incompatibilities:

1. Upstream's passthrough is intentional, not missing. For auth.type === "api", @ex-machina/opencode-anthropic-auth returns {} on purpose. Regular Console keys (sk-ant-api03-...) work fine without any transforms — so the plugin deliberately stays out of the way. Turning attestation transforms on for everyone upstream would silently change behavior for people whose keys currently work, for zero benefit to them and non-zero risk of breakage.

2. Body mutation of user-facing fields. This plugin strips temperature from every request (Claude Code never sends one, and strict-attestation servers reject requests that do). The upstream doesn't touch temperature. Doing this upstream would silently drop a field users might legitimately be setting.

3. Home-directory file I/O. This plugin reads ~/.claude.json on every request to resolve metadata.user_id. The upstream has no such dependency. Adopting it upstream would add a new side channel ("plugin reads files outside the project") that a general-purpose auth plugin probably shouldn't have by default.

4. Extra headers. This plugin sends x-app: cli; the upstream doesn't. Anthropic's server behavior can differ based on header presence, so adding it upstream risks regressing the OAuth flow that currently works.

5. Experimental A/B knobs. OPENCODE_ANTHROPIC_CONSOLE_TOOL_PREFIX=0 exists to probe Anthropic's attestation rules (exact tool-name matching vs mcp_ prefixing). That kind of experimental churn doesn't belong in a stable, widely-depended-on auth plugin.

6. Release cadence. Strict-attestation rules change on Anthropic's side with no notice. A side-car plugin can iterate on CLAUDE_CODE_VERSION, tool-name maps, and system-prompt anchors at its own pace without coordinating every tweak through the upstream's review cycle.

So the split isn't a fork or a disagreement — it's the right shape for the problem. Each plugin owns a distinct auth.type branch, they cooperate by construction, and the user opts into the extra behavior by installing an extra package. If @ex-machina/opencode-anthropic-auth ever decides to cover attested API keys natively (e.g. behind an explicit opt-in flag), this plugin can simply be deprecated — publishing it as a separate package doesn't block that merge.

Requirements

• opencode with the v1 plugin API (@opencode-ai/plugin)
• Node >= 20
• @ex-machina/opencode-anthropic-auth installed alongside (so its "Manually enter API Key" menu entry exists and so its OAuth flows keep working)
• A working Claude Code install is optional but recommended — see Identity source

Install

This plugin is designed to be installed together with @ex-machina/opencode-anthropic-auth.

From npm (once published)

// ~/.config/opencode/opencode.json
{
  "plugin": [
    "opencode-anthropic-console",
    "@ex-machina/opencode-anthropic-auth"
  ]
}

From a local checkout

git clone https://github.com/DusKing1/opencode-anthropic-console.git
cd opencode-anthropic-console
npm install
npm run build

{
  "plugin": [
    "file:///absolute/path/to/opencode-anthropic-console",
    "@ex-machina/opencode-anthropic-auth"
  ]
}

On Windows, use forward slashes or escape the backslashes:

{
  "plugin": [
    "file:///D:/GitHub/opencode-anthropic-console",
    "@ex-machina/opencode-anthropic-auth"
  ]
}

About plugin order

opencode deduplicates each plugin's auth.methods array by provider ID, so the last plugin to register for anthropic wins the opencode auth login anthropic menu. Listing @ex-machina/opencode-anthropic-auth after this plugin (as shown above) lets its richer menu (Claude Pro/Max, Create an API Key, Manually enter API Key) drive the login flow. Both plugins' loaders still run regardless of order, so the attestation transforms still apply on the auth.type === 'api' branch.

This plugin also ships a minimal stand-alone "Console API Key" login method so it remains usable without @ex-machina/opencode-anthropic-auth installed — but the recommended deployment is both plugins together.

Usage

1. Get your API key from https://console.anthropic.com/ (including Enterprise / Claude-Code-scoped keys).

2. Authenticate opencode:

   opencode auth login anthropic
   # pick "Create an API Key" or "Manually enter API Key" (both via @ex-machina/opencode-anthropic-auth)
   # or "Console API Key" (this plugin's fallback)
   # paste your sk-ant-api03-... key

   Or set it via environment:

   export ANTHROPIC_API_KEY=sk-ant-api03-...

3. Start opencode and pick an anthropic/claude-* model. Outgoing requests now carry the Claude Code attestation signature.

Identity source

Anthropic's attestation requires a metadata.user_id on every request. This plugin resolves one in the following order (first hit wins, result is cached):

1. OPENCODE_ANTHROPIC_CONSOLE_USER_ID env var
2. userID field in ~/.claude.json (written automatically by the Claude Code CLI on first login)
3. A deterministic synthetic value derived from $USERNAME/$HOSTNAME (fallback — prefer the real Claude Code value)

If you don't run Claude Code on this machine, run it once (claude -p hi) to create the file, or set the env var manually:

export OPENCODE_ANTHROPIC_CONSOLE_USER_ID=$(jq -r .userID ~/.claude.json)

You can also override the config path:

export OPENCODE_ANTHROPIC_CONSOLE_CLAUDE_JSON=/custom/path/.claude.json

What this plugin actually does

Activation gate: only when auth.type === "api". All other auth types pass through untouched, so @ex-machina/opencode-anthropic-auth keeps full control of its OAuth flows.

On every outgoing request to /v1/messages:

| Transform | Reason | |-----------|--------| | Set user-agent: claude-cli/<version> (external, cli) | Claude Code CLI identity | | Set x-app: cli | Distinguishes CLI traffic from web Claude (not sent by @ex-machina/opencode-anthropic-auth) | | Merge anthropic-beta with Claude Code's required beta flags | Matches Claude Code's feature surface | | Append ?beta=true to the URL | Claude Code always sends this | | Prepend the Claude Code identity block to system[] | The first paragraph of system must be Claude Code's identity | | Strip opencode-branded paragraphs from system[] | Otherwise two agents appear to speak | | Inject metadata.user_id | Required by attestation (not injected by @ex-machina/opencode-anthropic-auth) | | Remove temperature from the body | Claude Code never sends one; strict-attestation servers reject it | | Prefix tool names with mcp_ + PascalCase (e.g. mcp_Bash) | Matches Claude Code's tool naming convention | | Strip the mcp_ prefix from streaming SSE responses | So opencode's tool router recognises the names |

Keeps x-api-key as-is (standard Console key auth).

Environment variables

| Variable | Default | Purpose | |----------|---------|---------| | OPENCODE_ANTHROPIC_CONSOLE_USER_ID | — | Override metadata.user_id | | OPENCODE_ANTHROPIC_CONSOLE_CLAUDE_JSON | ~/.claude.json | Override Claude Code config path | | OPENCODE_ANTHROPIC_CONSOLE_TOOL_PREFIX | 1 | Set to 0 to send tool names without the mcp_ prefix (for A/B testing attestation) | | ANTHROPIC_BASE_URL | — | Route requests to a proxy or custom gateway | | ANTHROPIC_INSECURE | — | 1/true to skip TLS verification when ANTHROPIC_BASE_URL is set |

Troubleshooting

Request still fails with 429 rate_limit_error: "Error" — Attestation is rejecting some part of the request. Confirm:

• The plugin is installed and loaded (check opencode logs for plugin init).
• metadata.user_id is a 64-character hex string (copy from ~/.claude.json).
• Your CLAUDE_CODE_VERSION isn't too stale — see Roadmap.
• Capture the outgoing request with mitmproxy and diff against a real claude -p hi invocation.

401 invalid x-api-key — The key is wrong or was issued as an OAuth-tied key. Re-issue a Console API key.

400 metadata.user_id error — The synthetic fallback produced an invalid shape. Set OPENCODE_ANTHROPIC_CONSOLE_USER_ID explicitly.

400 tools does not match — Attestation may now require the literal Claude Code tool names instead of opencode's names prefixed with mcp_. Try OPENCODE_ANTHROPIC_CONSOLE_TOOL_PREFIX=0; if still failing, Claude Code's tool set and opencode's have diverged and deeper name remapping is needed (see Roadmap).

Verifying against real Claude Code traffic

The quickest way to audit this plugin's output is to sit both opencode and claude behind mitmproxy:

# Terminal 1
mitmproxy

# Terminal 2 — reference capture
HTTPS_PROXY=http://127.0.0.1:8080 claude -p "say hi"

# Terminal 3 — same via opencode
HTTPS_PROXY=http://127.0.0.1:8080 opencode

Any field present in the Claude Code capture but missing or different in the opencode capture is a bug here.

Roadmap

• [ ] Generate x-anthropic-billing-header (cc_version / cc_entrypoint / cch) — @ex-machina/opencode-anthropic-auth emits this on OAuth; attestation-strict keys may require it too
• [ ] Exact Claude Code tool-name matching (not just mcp_ prefixing)
• [ ] Periodic self-test that diffs against a recorded Claude Code reference capture
• [ ] Auto-refresh CLAUDE_CODE_VERSION from the installed Claude Code CLI

Acknowledgements

Transform logic is a clean-room re-implementation informed by @ex-machina/opencode-anthropic-auth and by public HackerNews discussion of Anthropic's Claude Code attestation.

License

MIT — see LICENSE.