SQLSRV_connect with windows authentication

I am trying to connect  a PHP 7.2.2 application to a SQL server database, using windows authentication, but am seeing this error

Array ( [0] => Array ( [0] => 28000 [SQLSTATE] => 28000 [1] => 18456 [code] => 18456 [2] => [Microsoft][ODBC Driver 17 for SQL Server][SQL Server]Login failed for user 'NT AUTHORITY\IUSR'. [message] => [Microsoft][ODBC Driver 17 for SQL Server][SQL Server]Login failed for user 'NT AUTHORITY\IUSR'. ) [1] => Array ( [0] => 28000 [SQLSTATE] => 28000 [1] => 18456 [code] => 18456 [2] => [Microsoft][ODBC Driver 17 for SQL Server][SQL Server]Login failed for user 'NT AUTHORITY\IUSR'. [message] => [Microsoft][ODBC Driver 17 for SQL Server][SQL Server]Login failed for user 'NT AUTHORITY\IUSR'. ) )

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Please advise on what to need to do to resolve the problem.
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Basically, it's saying that the NT AUTHORITY\IUSR is the user account that is being used to authenticate against the SQL server database, but that particular user does not have permissions to connect.

So either you aren't using the correct credentials or methodology to pass the correct credentials, or else you need to allow NT AUTHORITY\IUSR to connect.

Typically, this is because you're not correctly specifying credentials in your DB connection string, and so it's falling back to using the app pool user account (which usually runs as that IUSR user).

Here's a good article from Microsoft that expands on this:

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If you're getting the error "Login failed for user 'NT AUTHORITY\IUSR'", then your app is not using the account that you set up. It's passing along the user credentials from IIS, which in the case of allowing anonymous access is IUSR.

Other than making sure the account you set up has the appropriate access, this isn't really a SQL question. It's a matter of fixing your connection properties in your app.

Dave BaldwinFixer of ProblemsCommented:
"windows authentication" requires a logged in user on the machine where the SQL Server is.  You can not use it for a remote login, it just won't work.  SQL Authentication can be used for remote logins because it is just username and password.
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rwlloyd71Author Commented:
Thank you for all your comments.

To clarify, I understand that only allowing SQL to accept windows authentication makes the service more secure, so I was trying to not use an SQL login.

Your comments seem to suggest that my php application cannot connect with just windows authentication, so I will have to allow SQL logins and create an account to login with.

Is this correct?
rwlloyd71Author Commented:
On the other hand, by having a windows authentication, I may be granting too generous permissions on the whole database with my connection, so maybe I am better off with an SQL login...
Please make sure you read that blog from Microsoft. It covers this issue in-depth. However I would agree that using standard SQL login credentials is better for web apps due to the way that IIS runs. Integrated Windows auth is usually better suited for human users (just my general opinion - there will always be exceptions). Like you said, granting IUSR access to your DB would probably result in more access than you want.
Dave BaldwinFixer of ProblemsCommented:
For what it's worth, I use Windows Auth with SSMS and SQL Auth with my PHP applications on 4 different installs of SQL Server Express.
rwlloyd71Author Commented:
I am going to use an SQL login for my phone connection and windows for any direct database work with SSMS
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