I'm not sure why you would want to do that, as it is terribly insecure, but no, I don't believe that is possible. I'm quite certain the login page requires an HTTP POST. Most browsers will allow you to just save your username and password though if you're just looking for a way to speed up the login process. Is there some other reason you're wanting to do this?

Yes I have multiple website which are pretty similar but vary in content but they all have a distributor page which is the same. To see this page in the nav you have to log in or it is hidden. What I wanted to do was have a "master site" and use the Box Grabber add on to display content on the sub sites.

This works for normal pages but due to the fact you have to log in to see the distributor content box grabber wont display these pages. I figured seeing though the option only appears when you are logged in then that would counter any security threat and wanted to log in via URL so i can put that into the box grabber add on to give it access to the protected content.

I hope that made some sort of sense!!

How about a GUID attachment in the URL from a referring site?

We do these on custom sites to allow users who have already logged in on their site to pass through to ours without reentering credentials.