SQL Server Management Studio 2012, authentic multi-user login
You just need to create your user and assign it to login for accessing the database.

Assuming you want to have read/write access:

USE [master]
GO
CREATE LOGIN [Domain\User_name] FROM WINDOWS WITH DEFAULT_DATABASE=[master]
GO
USE [Database_name]
GO
CREATE USER [Domain\User_name] FOR LOGIN [Domain\User_name]
GO
USE [Database_name]
GO
EXEC sp_addrolemember N'db_datareader', N'Domain\User_name'
GO
USE [Database_name]
GO
EXEC sp_addrolemember N'db_datawriter', N'Domain\User_name'
GO