App Config - The Login Is From An Untrusted Domain

First, I try to connect to sql server of other computer(PC1-PC\Instance1) through ssms with Windows Authentication but got this error Login failed. The login is from an untrusted

Solution 1:

<connectionStrings><add name="LibrarySystem.Properties.Settings.LibraryConnectionString" connectionString="Data Source=PC1-PC\Instance1;
 Initial Catalog=System1;MultipleActiveResultSets=True;User id = sa;Password = 1234" providerName="System.Data.SqlClient"/>