After seeing posts about auto-login programs and hearing "encrypted" or "in a text file" I started searching the World of Warcraft folder.
Inside the WTF Folder I opened the "Config" Folder.
I scrolled through it and near the end I found the section that puts my username in the username spot of the log in screen everytime I open WoW.
My thoery is im thinking you can maybe put in something similar to "[Square]Set password "xxxxxxxxxx" and it will always be pre-typed.
I have tryed copy pasting "[Square]Set password "xxxxxxxxxx" and it didnt work but maybe someone from the MMOwned community can make something of this.