Per-user encryption

[thyseus]

Hey,

thanks for this great extension. In 2015 you wrote:

The current version currently uses a global key for encryption, but in the future I will add an easy way to do per-user encryption.

The only issue with per-user encryption is that you need to generate and store the user key otherwise you'd obviously lose the data. I just want to think about the best approach to include that without either assuming too much stuff or increasing the coupling.

I will probably release a new version next week with per-user encryption anyway!

How about using a PHP callback function to determine the current necessary password, like this:

'password' => function() { return Yii::$app->user->secret; }

Of course, the user needs to ensure that his secret never changes over time.