We have a test and staging environment. Do I need to get multiple app keys? Our test and staging environments block incoming traffic that does not originate from our office. Does domain verification only occur once on creation or will yahoo ping the empty html file?
Are you setting up an open or oauth application? I'm guessing that since you're asking about the domain verification you are trying to register an OAuth application (if not please let me know). With an OAuth application you are going to have a few problems with this setup:
If the domain name that you registered is different than the URL being used for the test environment, the OAuth flow will fail
Since that is the case you will need to set up multiple keys. To register these test domains the location has to be publicly accessible. Since your servers are blocking incoming traffic that process will fail.
If you are using custom ports or an ip address for the staging / test environment, that will also cause problems with the domain registration as those are both restricted.
All in all, I would suggest building your application on an unlinked production location.
Jonathan LeBlanc Technology Evangelist Yahoo! Developer Network Twitter: jcleblanc