When accessing the K2 Designer and Workspace sites, a HTTP Error 402.2 - Unauthorized appears

This article was created in response to a support issue logged with K2. The content may include typographical errors and may be revised at any time without notice. This article is not considered official documentation for K2 software and is provided "as is" with no warranties.
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Issue

When accessing the K2 Designer and Workspace sites from the browser, the following error appears:

"HTTP Error 401.2 Unauthorized: You are not authorized to view this page due to invalid authentication headers." 

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Symptoms

When opening IIS manager > Sites > K2 site > Workspace/Designer App > Authentication, Windows Authentication is missing.

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Troubleshooting Steps

To resolve the issue, ensure that the 'Windows Authentication' role service is installed on the server and then, enable Windows authentication for the site or application. 

Please see this Microsoft article for more information on how to verify/install this service.