I use windows 7. I have had this problem intermittently over the past year several years. I was going through months at a time when itunes was asking to enter passwords every time I opened it, sometimes once to "check for automatic downloads" and sometimes an additional time to "sign into my itunes account.' thankfully it would "just go away" after a while, but then would re-occur. after the latest re-occurrence it finally got sooooo annoying I took a full day to fix the problem, which took multiple calls with apple, and a bunch of wild goose chases which included re-installing itunes. Just by luck it seems, I finally found one person at apple who solved the problem. In my case it was simple. All we had to do was de-authorize the computer and re- authorize it (which you can do by clicking the "store" drop down in the menu bar, top left, and dropping down to the de-authorize or authorize line)
the explanation from the tech support person: itunes gets out of whack with the apple servers and does not know your computer is authorized (even thought you can play your itunes content, so the issues is completely camouflaged.) I don't completely understand this, but who cares, the problem is solved. I do not use safari, and it seems there may be other causes of and fixes for this problems for people who do. Not sure it the "fix" for me will work for others, but I hope so. good luck!!!!
