> For the complete documentation index, see [llms.txt](https://developer.ultimo.net/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://developer.ultimo.net/api-guide/rest/additional-security.md).

# Additional security

For cloud customers on Azure, additional security is available for the REST API. Without additional security measures, anyone in possession of the API key secret is able to connect to the API endpoint.

## IP filtering

It is possible to add IP address range validations per API key. Use '-' to allow everything in between and ';' to use multiple ranges. Keep in mind: this is a whitelist. All IP addresses not on the whitelist will not be able to connect.

Support for both IPv4 and IPv6 address range validation is available. When only one of them is filled, the other is completely blocked. Example: when IPv4 is filled, no one can connect with a IPv6 address.

Note: IP filtering on API keys have no relation with IP filtering options for logging on to the Ultimo application.

## Client certificates

It is possible to specify a certificate thumbprint per API key. The client connecting to the API endpoint should always send the certificate that meets the certificate thumbprint on the API key when sending a request.

When a certificate thumbprint is used on an API key, the URL of the API endpoint is different than without a client certificate. Instead of using the standard URL:

> <https://customer.ultimo.net/api/v1/>

Use the following URL:

> https\://**api-**&#x63;ustomer.ultimo.net/api/v1/

A cUrl command example of sending a request with a client certificate:

```
curl --cert C:\temp\client.crt --key c:\temp\client.key -X GET "https://api-customer.ultimo.net/api/v1/object/Article" -H "accept: application/json" -H "ApiKey: [ApiKey]"
```


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