ASP.NET: 401 unauthorized access is denied due to invalid credentials

Solution 1: (this will end up with @User.Identity.IsAuthenticated be empty string)

• In IIS, select the website you're having the issue with.
• In the IIS section, select 'Authentication'.
• Right click on Anonymous Authentication and select 'Edit'
• Check the 'Specified User' radio button and click on 'Set'
• I entered my username, password and password confirmation and click ok.

Fix:“401 – Unauthorized: Access is denied due to invalid credentials“ on ASP.NET MVC & IIS 7
https://support.microsoft.com/en-ca/kb/871179

ASP.NET: Identity not using Windows NT

Things to check

1) what is set in the web.config, windows authentication?

 mode="Windows" />

    users="?"/>

impersonate="false" />

2) Is anonymous access in IIS disabled? (enable Windows Authentication)
3) Try HttpConext.Current.User instead of Thread.CurrentPrincipal

ASP.NET: Login failed for user 'DOMAIN\MACHINENAME$'

Symptom: 

Root cause: web application is using the account which doesn't have access to connect to SQL server

Solution:

1. add "NT AUTHORITY\NETWORK SERVICE" as SQL Server login, allow it to access the database (in the "User Mapping", assign the db_owner role for the corresponding databases)
2. in IIS, create a custom application pool which is using "NetworkService" as Identity (make sure to use Integrated pipeline). then change the web application to use this pool