To do this, invoke Siri, then say "Wolfram password," or "Wolfram Alpha password." This retrieves an 8-character random password, along with a list of a half-dozen others. You can also have Siri get longer passwords, if eight characters doesn't ring your bell. Say, "Wolfram 14-character password," for example.
The downside to this is that you can't copy this password, and once you've switched away from the Siri results, you can't get them back again. So you need to either type this password on a computer or other iOS device, or write it down. Either way, make sure you delete it, or store it in some sort of encrypted file.

