sqlsrv_connect: use Windows authentication?
As stated in the documentation you do not pass the UID and PWD to utilize Windows Authentication. You can see an example here.

From remarks within documentation link:


  If values for the UID and PWD keys are not specified in the optional $connectionInfo parameter, the connection will be attempted using Windows Authentication. For more information about connecting to the server, see How to: Connect Using Windows Authentication and How to: Connect Using SQL Server Authentication.