FYI, when we say ‘svn auth data’, we are meaning the private security data that SVN uses. This is separate and distinct form the URL and other login details that the Editor uses, so the fact that your URL is still present in the login dialog is not important.
As you are on Mac, you may however be suffering from this issue that was reported recently:
https://answers.unrealengine.com/questions/58947/svn-with-assemble-os-x-bad-request.html
We are looking into upgrading the version of SVN that we ship with the Editor to address this issue.