The client should not ask for the user name either if the SVN_SSH environment variable is declared with the user name. The client should not ask for the password if the pageant.exe is up and running with has been correctly setuped private key.
Svn client using these general steps related to the native Windows svn.exe (should not be a ported one, for example, like the msys or cygwin tools which is not fully native): In case of in the Windows usage you have to setup the ssh key before run the The svn+ssh protocol must be setuped using both the private and the public ssh key.