[andrewreds]

A password works by there is a piece of text that only you know, and thus, when you give that password to a server, that server knows who you are.

can't you also view a url as a password? (If only I know the url, then only I can download the file).

I am able to give out a url to someone else, so they can access the file, likewise, I can give out my file server's username and password, and whoever has it can also access my files.

[gizzlon]

You have a point, but the difference is that url's are not usually considered secret and are therefore not treated the same way a password would be. For example in the browser..

[piaskal]

Google is already storing urls to those files.