Is there a particularly easy method to doing this?
Are you playing on Console or PC?
If on console, get some keys in your inbox from entering shift codes online. I lost everything in my bank randomly, had a bunch of legendary weapons. I emailed support and complained about it, they sent me 25 gold keys because they couldn't recover what I lost. I used those 25 keys to do the glitch and amass 500+ keys in 10 minutes. You could always email them and tell them you lost weapons and they will send you some free golden keys.
Once you have a few, while in a game, go into your settings and set your network settings to offline. Go back to the game and claim the codes in your inbox. Then quit your game back to the main menu and choose you continue your game. Once you load back in, go back to your inbox and the keys will be back, and you will have whatever you claimed. Just keep repeating these steps until you build up a ton of keys.