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# Authenticate with Windows NTLM authentication in Postman

Windows NTLM is the authorization flow for the Windows operating system and for standalone systems. NTLM is a challenge-response style authentication protocol.

To use NTLM authentication, do the following:

1. In the **Authorization** tab for a request, select **NTLM Authentication** from the **Auth Type** dropdown list.

2. Enter your **Username** and **Password** for NTLM access. You can optionally set advanced details, but Postman will try to generate values for them if necessary.

By default, your request will run a second time after extracting data received from the first request. You can turn off this behavior by selecting the **Yes, disable retrying the request** checkbox.

Advanced parameters for NTLM auth are as follows:

* **Domain** - The domain or host to authenticate against.
* **Workstation** - The hostname of your PC.