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

# Authentication

> Learn about the authentication methods provided by Smartbills, including OAuth2 flows for secure access.

## Getting Started

To begin, you will need to create an API key from your Smartbills dashboard or contact us to obtain an API key. Head to [https://developers.smartbills.io](https://developers.smartbills.io)

### Connected Accounts

To act on behalf of connected accounts, clients can make requests using the special `on-behalf-of` header. Ensure that this header contains a valid Smartbills account ID.

## OAuth2 Authentication

### Client Credentials Flow

Use this flow for server-to-server communication.

**Endpoint:** `https://api.smartbills.io/connect/token`

**Request:**

```http theme={null}
POST /connect/token HTTP/1.1
Host: api.smartbills.io
Content-Type: application/x-www-form-urlencoded

grant_type=client_credentials&client_id=YOUR_CLIENT_ID&client_secret=YOUR_CLIENT_SECRET
```

**Response:**

```json theme={null}
{
  "access_token": "YOUR_ACCESS_TOKEN",
  "token_type": "Bearer",
  "expires_in": 3600
}
```

#### Code Example

<CodeGroup>
  ```javascript JavaScript theme={null}
  import { SBClient } from "@smartbills/sdk"

  const client = new SBClient();
  const tokenResponse = await client.auth.getToken({
    grant_type: "client_credentials",
    client_id: "YOUR_CLIENT_ID",
    client_secret: "YOUR_CLIENT_SECRET"
  });
  ```

  ```csharp C# theme={null}
  using Smartbills.NET;

  var client = new SBClient();
  var tokenResponse = await client.Auth.GetTokenAsync(new TokenRequest
  {
      GrantType = "client_credentials",
      ClientId = "YOUR_CLIENT_ID",
      ClientSecret = "YOUR_CLIENT_SECRET"
  });
  ```
</CodeGroup>

### Authorization Code Flow

Use this flow for user authentication.

**Step 1: Redirect to Authorization Endpoint**

```http theme={null}
GET /connect/authorize?response_type=code&client_id=YOUR_CLIENT_ID&redirect_uri=YOUR_REDIRECT_URI&scope=YOUR_SCOPES
Host: api.smartbills.io
```

**Step 2: Exchange Authorization Code for Access Token**

```http theme={null}
POST /connect/token HTTP/1.1
Host: api.smartbills.io
Content-Type: application/x-www-form-urlencoded

grant_type=authorization_code&code=AUTHORIZATION_CODE&redirect_uri=YOUR_REDIRECT_URI&client_id=YOUR_CLIENT_ID&client_secret=YOUR_CLIENT_SECRET
```

**Response:**

```json theme={null}
{
  "access_token": "YOUR_ACCESS_TOKEN",
  "token_type": "Bearer",
  "expires_in": 3600,
  "refresh_token": "YOUR_REFRESH_TOKEN"
}
```

#### Code Example

<CodeGroup>
  ```javascript JavaScript theme={null}
  import { SBClient } from "@smartbills/sdk"

  const client = new SBClient();
  const tokenResponse = await client.auth.getToken({
    grant_type: "authorization_code",
    code: "AUTHORIZATION_CODE",
    redirect_uri: "YOUR_REDIRECT_URI",
    client_id: "YOUR_CLIENT_ID",
    client_secret: "YOUR_CLIENT_SECRET"
  });
  ```

  ```csharp C# theme={null}
  using Smartbills.NET;

  var client = new SBClient();
  var tokenResponse = await client.Auth.GetTokenAsync(new TokenRequest
  {
      GrantType = "authorization_code",
      Code = "AUTHORIZATION_CODE",
      RedirectUri = "YOUR_REDIRECT_URI",
      ClientId = "YOUR_CLIENT_ID",
      ClientSecret = "YOUR_CLIENT_SECRET"
  });
  ```
</CodeGroup>