'Login failed for user 'NT AUTHORITY\IUSR'

Message from ExternalSystem: ‘Login failed for user ‘NT AUTHORITY\IUSR’.’.

 This error occurs because database does recognize the credentials passed from SharePoint. Which database? Database that you are connecting to in your external content type! It depends on you have setup application pool identity in SharePoint. If you are not using managed service account for your services, you are most likely to get this error. This is not likely to occur in corporate environments but in home or test environments where users use LOCAL SYSTEM OR NETWORK SERVICE in application pools, this error will occur. This is because NETWORKSERVICE translates to NTAUTHORITY\IUSR when credentials are passed from web server to database server. IUSR is used when user credentials are not available, for example, for anonymous users. To resolve this problem, either change application pool identity or add NT AUTHORITY\IUSR to the database permissions. The first scenario is quite common. You can change application pool identity by go to the web server and updating application pools or by logging into SharePoint central admin site and going to ManageService Accounts. We will cover second scenario here, that is, to add IUSR to the database.

1.      Go to MicrosoftSQL Server Management Studio and connect to your database server.

2.      Expand Security node and right-click Logins node and select New Login.

3.      In the LoginName, enter IUSR and click Search…. This will open a new search box. Enter IUSR in the object name and click Check Names. Click OK.

4.      You will notice that Login Name has been populated with MACHINENAME\IUSR where MACHINENAME is your machine name, for example, in the figure below, you see SP2013\IUSR. SP2013 is my machine name.

This is not what you want to add to the logins. Change MACHINENAME to NT AUTHORITY so Login Name should read NT AUTHORITY\IUSR. Click OK.

5.      Now you may think that the user has been added and your external content type will work. Right? Wrong! You still have to map user to the database otherwise you will get following error on the list page(where you are trying to load external content type):

The query against the database caused an error.

 

 

 

This error occurs, as I said, because user is not mapped to the database yet.

6.      To map user to the database, right-click NT AUTHORITY\IUSR in Logins and select Properties.

 

 

7.      There are two ways to do this mapping. One way is to add user to one of the server roles, for example,  serveradminor sysadmin. This will give user full rights to all databases and thus you won’t have to do explicit mapping. To do this, on the properties page, click ServerRoles and check sysadmin. Click OK. Obviously you would not want to do this in real environment. So the other option is to map the user directly to the database that has been used in the external content type.

To add user mapping, in LoginProperties, click User Mapping. Locate the database in the list and then check the box in the Map column. As soon as you check the box, NT AUTHORITY\IUSER appears in the User column. That’s it. Click OK to save the setting. By the way on the same properties page, you can also assign database role membership to the user for the database but that is not required.

Now, go back to the list page and reload it. You will see results from the external data source.