Keep real keys private with LangChain.

# pip install langchain langchain-openai deny-sh requests
import os, requests, json
from langchain.agents import create_agent
from langchain.tools import tool
from langchain_openai import ChatOpenAI
from deny_sh import vault_get

@tool
def get_invoice(id: str) -> str:
    """Look up a Stripe invoice by id."""
    # resolve the credential INSIDE the tool boundary
    stripe_key = vault_get("stripe-prod", os.environ["VAULT_PW"])
    r = requests.get(f"https://api.stripe.com/v1/invoices/{id}",
        headers={"Authorization": f"Bearer {stripe_key}"})
    # narrowed DTO: never return raw upstream response bodies
    body = r.json()
    return json.dumps({"id": body.get("id"), "amount_due": body.get("amount_due"),
        "status": body.get("status")})

agent = create_agent(
    model=ChatOpenAI(model="gpt-5.4"),
    tools=[get_invoice],
    system_prompt="You are a billing assistant.",
)
result = agent.invoke({"messages": [
    {"role": "user", "content": "Look up invoice in_1Abc123XYZ"},
]})
print(result["messages"][-1].content)

// npm install langchain @langchain/openai deny-sh@^2.2.0 zod
import { createAgent, tool } from 'langchain';
import { ChatOpenAI } from '@langchain/openai';
import { vaultGet } from 'deny-sh/client';
import { z } from 'zod';

const invoiceTool = tool(
  async ({ id }) => {
    // resolve the credential INSIDE the tool boundary
    const stripeKey = await vaultGet('stripe-prod', process.env.VAULT_PW!);
    const r = await fetch(`https://api.stripe.com/v1/invoices/${id}`, {
      headers: { Authorization: `Bearer ${stripeKey}` }
    });
    // narrowed DTO: never return raw upstream response bodies
    const body = await r.json();
    return JSON.stringify({ id: body.id, amount_due: body.amount_due, status: body.status });
  },
  {
    name: 'get_invoice',
    description: 'Look up a Stripe invoice by id',
    schema: z.object({ id: z.string() }),
  }
);

const agent = createAgent({
  model: new ChatOpenAI({ modelName: 'gpt-5.4' }),
  tools: [invoiceTool],
  systemPrompt: 'You are a billing assistant.',
});

const result = await agent.invoke({
  messages: [{ role: 'user', content: 'Look up invoice in_1Abc123XYZ' }],
});
console.log(result.messages[result.messages.length - 1].content);

def tools_for_tenant(tenant_id, tenant_pw, tenant_api_key):
    @tool
    def get_invoice(id: str) -> str:
        """Look up a Stripe invoice for this tenant."""
        stripe_key = vault_get("stripe-prod", tenant_pw,
            api_key=tenant_api_key)
        ...  # same shape as above, narrowed DTO returned
    return [get_invoice]

# per-request: build the agent fresh with this tenant's tools
agent = create_agent(model=llm, tools=tools_for_tenant(tid, pw, key))