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Sample: Passing User Token from Agent State to MCP via ContextToEnvMapperCallback

This sample demonstrates how to use the context_to_env_mapper_callback feature in ADK to pass a user token from the agent's session state to an MCP process (using stdio transport). This is useful when your MCP server (built by your organization) requires the same user token for internal API calls.

How it works

  • The agent is initialized with a MCPToolset using StdioServerParameters.
  • The context_to_env_mapper_callback is set to a function that extracts the user_token from the agent's state and maps it to the USER_TOKEN environment variable.
  • When the agent calls the MCP, the token is injected into the MCP process environment, allowing the MCP to use it for internal authentication.

Directory Structure

contributing/samples/stdio_mcp_user_auth_passing_sample/
├── agent.py       # Basic agent setup
├── main.py        # Complete runnable example
└── README.md

How to Run

Option 1: Run the complete example

cd /home/sanjay-dev/Workspace/adk-python
python -m contributing.samples.stdio_mcp_user_auth_passing_sample.main

Option 2: Use the agent in your own code

from contributing.samples.stdio_mcp_user_auth_passing_sample.agent import create_agent
from google.adk.sessions import Session

agent = create_agent()
session = Session(
    id="your_session_id",
    app_name="your_app_name", 
    user_id="your_user_id"
)

# Set user token in session state
session.state['user_token'] = 'YOUR_ACTUAL_TOKEN_HERE'
session.state['api_endpoint'] = 'https://your-internal-api.com'

# Then use the agent in your workflow...

Flow Diagram

graph TD
    subgraph "User Application"
        U[User]
    end
    
    subgraph "Agent Process"
        A[Agent Instance<br/>per user-app-agentid]
        S[Session State<br/>user_token, api_endpoint]
        C[ContextToEnvMapperCallback]
    end
    
    subgraph "MCP Process"
        M[MCP Server<br/>stdio transport]
        E[Environment Variables<br/>USER_TOKEN, API_ENDPOINT]
        API[Internal API Calls]
    end
    
    U -->|Sends request| A
    A -->|Reads state| S
    S -->|Extracts tokens| C
    C -->|Maps to env vars| E
    A -->|Spawns with env| M
    M -->|Uses env vars| API
    API -->|Response| M
    M -->|Tool result| A
    A -->|Response| U
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Context

  • Each agent instance is initiated per user-app-agentid.
  • The agent receives a user context (with token) and calls the MCP using stdio transport.
  • The MCP, built by the same organization, uses the token for internal API calls.
  • The ADK's context-to-env mapping feature makes this seamless.