I recently did a project involving MS SQL server native user and login management. This is is the Script that i used to create the SP needed.
CREATE PROC [dbo].[usp_CreateLoginAndUser]
@Login sysname,
@Password sysname
AS
DECLARE @CreateLoginStatement nvarchar(200)
SET @CreateLoginStatement = 'CREATE LOGIN ' +
QUOTENAME(@Login) +
' WITH PASSWORD = ' +
QUOTENAME(@Password, '''')+';'+
' CREATE USER ' +
QUOTENAME(@Login) +
' FOR LOGIN ' +
QUOTENAME(@Login) +';'
EXEC sp_executesql @CreateLoginStatement
this SP creates a MS SQL server User login and a database User at the same time.