This sample demonstrates how headless agent's tools can leverage Auth0's Client-Initiated Backchannel Authentication (CIBA) flow to request user authorization via push notification and obtain tokens for accessing separate APIs.

Additionally, it shows agent-level authorization via the OAuth 2.0 Client Credentials flow.

Allows an A2A client to securely interact with an external HR agent owned by the fictional company Staff0 to verify whether the provided user data corresponds to an active employee.

With the authorization of the employee involved (via push notification), the Staff0 HR agent can access the company's internal HR API to retrieve employment details.

sequenceDiagram
   participant Employee as John Doe
   participant A2AClient as A2A Client
   participant Auth0 as Auth0 (staff0.auth0.com)
   participant HR_Agent as Staff0 HR Agent
   participant HR_API as Staff0 HR API

   A2AClient->>HR_Agent: Get A2A Agent Card
   HR_Agent-->>A2AClient: Agent Card
   A2AClient->>Auth0: Request access token (Client Credentials)
   Auth0-->>A2AClient: Access Token
   A2AClient->>HR_Agent: Does John Doe with email jdoe@staff0.com work at Staff0? (Access Token)
   HR_Agent->>Auth0: Request access token (CIBA)
   Auth0->>Employee: Push notification to approve access
   Employee-->>Auth0: Approves access
   Auth0-->>HR_Agent: Access Token
   HR_Agent->>HR_API: Retrieve employment details (Access Token)
   HR_API-->>HR_Agent: Employment details
   HR_Agent-->>A2AClient: Yes, John Doe is an active employee.

• Python 3.12 or higher
• UV
• Gemini API key
• An Auth0 tenant with the following configuration:
  • APIs
    • HR API
      • Audience: https://staff0/api
      • Permissions: read:employee
    • HR Agent
      • Audience: https://staff0/agent
      • Permissions: read:employee_status
  • Applications
    • A2A Client
      • Grant Types: Client Credentials
      • APIs: HR Agent (enabled permissions: read:employee_status)
    • HR Agent
      • Grant Types: Client Initiated Backchannel Authentication (CIBA)
      • APIs: Auth0 Management API (enabled permissions: read:users)
  • Push Notifications using Auth0 Guardian must be enabled.
  • A test user enrolled in Guardian MFA.

1. Create a .env file by copying .env.example, and provide the required environment variable values.

2. Start HR Agent and HR API:

   uv run --prerelease=allow .

3. Run the test client:

   uv run --prerelease=allow test_client.py

Important: The sample code provided is for demonstration purposes and illustrates the mechanics of the Agent-to-Agent (A2A) protocol. When building production applications, it is critical to treat any agent operating outside of your direct control as a potentially untrusted entity.

All data received from an external agent—including but not limited to its AgentCard, messages, artifacts, and task statuses—should be handled as untrusted input. For example, a malicious agent could provide an AgentCard containing crafted data in its fields (e.g., description, name, skills.description). If this data is used without sanitization to construct prompts for a Large Language Model (LLM), it could expose your application to prompt injection attacks. Failure to properly validate and sanitize this data before use can introduce security vulnerabilities into your application.

Developers are responsible for implementing appropriate security measures, such as input validation and secure handling of credentials to protect their systems and users.