> ## Documentation Index
> Fetch the complete documentation index at: https://developers.calendbook.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Partner Authentication (M2M)

## How it works

Machine-to-Machine (M2M) authentication allows backend services and partner platforms to connect to our API **without user interaction**.\
This flow uses a **Broker Token** (also referred to as an API Key) to request a short-lived access token.

> ⚠️ We provide **custom authentication flows for partners**.\
> This documentation describes the **abstract flow** your exact implementation may vary depending on your integration and assigned scopes.

## Authentication Flow

1. **Obtain a Broker Token**
   * You’ll receive a Broker Token during the partner onboarding process.
   * The Broker Token is **rotated periodically** for security. You will be notified when a new one is issued.
   * Treat this token as a credential: it should only be stored in secure server-side environments.

2. **Request an Access Token**
   * Call the `/tokens` endpoint with your Broker Token.
   * The response includes a short-lived `access_token`, which you will use in subsequent API calls.

3. **Call the API**
   * Use the `access_token` in the `Authorization` header with the `Bearer` scheme for all API requests.