If you want to use SQL 2012 or above to backup directly to a URL and your servers are behind a corporate proxy that also requires auth, create the following .net config file so that the sql service will make the connection correctly:

c:\Program Files\Microsoft SQL Server\MSSQL11.MSSQLSERVER\MSSQL\Binn\BackuptoURL.exe.config

Add the following code with your proxy address to the new file:

<?xml version ="1.0"?>
      <proxy  proxyaddress="http://proxylb.domain.local:8080" bypassonlocal="true" usesystemdefault="True" />
        <add address="[a-z]+.domain.local$" />