Put MCP behind a gateway

klens does not sign anyone in on /mcp. To share the tools, put an MCP gateway in front of mcp.bind. The gateway signs each person in, decides which tools they may call, and forwards their calls to klens with a shared secret. klens answers only calls that carry the secret.

Set the shared secretCopy Anchor Link

1. Create a secret of at least 32 bytes.

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   openssl rand -base64 48

2. Pass it to klens and name it in mcp.secret.

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   mcp:
     bind: 0.0.0.0:8090
     secret: {env: KLENS_MCP_SECRET}
     privileges: [records, topic_configs, broker_configs, schema_text, acls]
     clusters: [dev, staging]

3. Configure the gateway to send the secret on every call it forwards, as the header Authorization: Bearer <secret>.

4. Point the gateway at mcp.bind. On Kubernetes, the chart serves it as the Service <release>-mcp, at http://<release>-mcp.<namespace>.svc:8090/mcp.

klens answers a call without the secret with 403 NOT_FROM_GATEWAY. A call with the secret may carry any Origin, because the gateway forwards the client's own and a web page cannot learn the secret.

With auth, mcp.secret is required. Without auth, the secret guards only the MCP port, so keep the UI port off every network the gateway serves.

Decide who may call which toolCopy Anchor Link

Every call that carries the secret holds the whole ceiling of the mcp block, whoever signed in at the gateway. klens roles do not apply to /mcp. The gateway decides who reaches the tools.

• Set mcp.privileges and mcp.clusters to the most that any person needs.
• Use the rules of the gateway to offer the write tools, klens_topic_create, klens_record_produce, and klens_schema_register, only to the people who need them.

Find who made a changeCopy Anchor Link

klens logs each change an agent makes, as it logs a change from the UI, without a user. A client that names itself in each request appears on the line as unverified:<name>. The log of the gateway names the person who made the call.

Connect clients through the gatewayCopy Anchor Link

Give each client the address of the gateway for /mcp, in place of the address of klens. A client signs its user in at the gateway on the first call, so register the redirect URIs of each client where the gateway signs people in.

The claude.ai and Claude Desktop connectors call from Anthropic's cloud, from addresses in 160.79.104.0/21. They reach klens only through a gateway that the internet can reach.