I would like to set the URL to whatever value it uses when I invite a user from the interface, however, the parameter InviteRedirectUrl does not provide a default value and it is required.
I've tried testing it by sending myself an invite and it looks as though I'm redirected to https://account.activedirectory.windowsazure.com/...
Is this to be expected? Is there a better option?
InviteRedirectUrl is the URL to which the invited user is forwarded after accepting the invitation. You can use your webapp website, such as https://myapps.azure.com/.
If you invite the guest user from Azure portal, it will be redirected to https://account.activedirectory.windowsazure.com/ by default.