Steps:
1. Open the Steam folder ( example C:\Program Files (x86)\Steam\ )
2. Create a new text file and then rename it and change the extension to name.cmd
(alternatively open notepad, and then save as, put All files at the bottom and save it as name.cmd always inside the Steam folder)
3. Write inside the file
Where user stands for your Steam username and password your password
4. Finished, now create a shortcut to this file on your desktop for convenience:
right click on the file -> send to -> Desktop (create shortcut)
If you want, change the icon and rename the link to whatever you want.
Video example:
