> For the complete documentation index, see [llms.txt](https://docs.elimity.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.elimity.com/reference-manual/v3.44.2/server-configuration/oauth2-endpoint-parameters-for-gateway-authentication.md).

# OAuth2 endpoint parameters for gateway authentication

The v3.42.0 release added a new `GatewayOAuth2EndpointParams` configuration option to support customization of Elimity Insights' access token retrieval for gateway authentication. By default, assuming `EnableGatewayOAuth2` is `true`, Elimity Insights will perform a basic OAuth2 client credentials flow. The `GatewayOAuth2EndpointParams` configuration option allows inclusion of additional parameters in the access token request. It should be a record mapping parameter names to [Expr](https://expr-lang.org/) programs that result in the respective parameter's value.

As an example we'll explain how this feature allows us to provide out-of-the-box gateway authentication to our SaaS customers. As detailed in [our documentation about gateway-based imports](/reference-manual/v3.44.2/advanced-topics/gateway-based-imports.md), we want to include `base_url`, `gateway_url` and `source_id` custom claims in the access tokens from our own OAuth2 server. To achieve this, we first need to make sure Elimity Insights provides the additional information in its token requests. For example, a token request from `https://example.elimity.com` for a gateway at `https://gateway.example.com` to import into a source with id `42` should look like this:

```http
POST /oauth/token HTTP/1.1
Host: auth.elimity.com
Content-Type: application/x-www-form-urlencoded

grant_type=client_credentials&
client_id=example-client-id&
client_secret=example-client-secret&
audience=gateway&
base_url=https%3A%2F%2Fexample.elimity.com&
gateway_url=https%3A%2F%2Fgateway.example.com&
source_id=42
```

This corresponds to the following configuration for Elimity Insights:

| Configuration option                      | Value                                    |
| ----------------------------------------- | ---------------------------------------- |
| `EnableGatewayOAuth2`                     | `true`                                   |
| `GatewayOAuth2ClientId`                   | `"example-client-id"`                    |
| `GatewayOAuth2ClientSecret`               | `"example-client-secret"`                |
| `GatewayOAuth2EndpointParams.audience`    | `"'gateway'"`                            |
| `GatewayOAuth2EndpointParams.base_url`    | `"baseURL"`                              |
| `GatewayOAuth2EndpointParams.gateway_url` | `"gatewayURL"`                           |
| `GatewayOAuth2EndpointParams.source_id`   | `"sourceID"`                             |
| `GatewayOAuth2TokenUrl`                   | `"https://auth.elimity.com/oauth/token"` |

Each value in the `GatewayOAuth2EndpointParams` record must be a valid [Expr](https://expr-lang.org/) program with result type `string`. Elimity Insights will inject the following variables:

| Variable     | Type     | Description                                         |
| ------------ | -------- | --------------------------------------------------- |
| `baseURL`    | `string` | Base URL of the Elimity Insights server             |
| `gatewayURL` | `string` | URL of the gateway to import data from              |
| `sourceID`   | `string` | Unique identifier of the source to import data into |


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