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

# Authentication

## Methods

The iinked Sign API supports two authentication methods, depending on how you are integrating:

* **OAuth 2.0** – For integrations that access data on behalf of your customers
* **API Keys** – For server-to-server access to your own organization’s data

Choose the method that matches your use case.

## OAuth 2.0 (Accessing Customer Accounts)

Use **OAuth 2.0** when you are building an integration that connects to **other users’ accounts**.

### When to Use OAuth

* You are a third-party developer building an app or integration
* Your app connects to multiple customer accounts
* Each customer authorizes your app individually
* You need scoped, permission-based access

See the [OAuth workflow guide](/v4/oauth) for more information.

<Note>
  iinked Sign access tokens are obtained through the OAuth 2.0 authorization process.
</Note>

**Request Header**

```http theme={null}
Authorization: Bearer <TOKEN>
```

## API Keys (Accessing Your Own Organization)

Use an **API key** when accessing data that belongs only to your own organization.

### When to Use an API Key

* Internal tools or backend services
* No third-party user authorization required
* Accessing only your organization’s data

<Tip>
  iinked Sign API Keys are available in your iinked Sign account under `Settings` > `Integration` > `API Keys`.
</Tip>

**Request Header**

```http theme={null}
api_key: <API_KEY>
```

## Datacenters

## Sandbox instances

### US

API endpoint: `https://sandbox.syngrafii.com/api/v1`\
API key management: [https://sandbox.syngrafii.com/integration](https://sandbox.syngrafii.com/integration)

### EU

API endpoint: `https://sandbox.syngrafii.eu/api/v1`\
API key management: [https://sandbox.syngrafii.eu/integration](https://sandbox.syngrafii.eu/integration)

## Production instances

### US

API endpoint: `https://sign.syngrafii.com/api/v1`\
API key management: [https://sign.syngrafii.com/integration](https://sign.syngrafii.com/integration)

### CA

API endpoint: `https://sign.syngrafii.ca/api/v1`\
API key management: [https://sign.syngrafii.ca/integration](https://sign.syngrafii.ca/integration)

### EU

API endpoint: `https://sign.syngrafii.eu/api/v1`\
API key management: [https://sign.syngrafii.eu/integration](https://sign.syngrafii.eu/integration)

## Private instances

API endpoint: `https://yourinstance.syngrafii.com/api/v1`\
API key management: `https://yourinstance.syngrafii.com/integration`

<Note>
  Replace `yourinstance` with the subdomain of your private instance.
</Note>