Remove dynamic parameters stored in session on subsequent auth
Hello,

I had a question about an issue that I'm experiencing with Grant right now (using grant-express 4.5.2, but it appears to function the same way in 5.x) ... when I authenticate to a `/connect` based endpoint that has been configured to use `dynamic` parameters, they will be properly stored into the session. However, on subsequent auth requests to other providers, the `dynamic` config sticks around in the session unless manually removed. This is true even if I explicitly unset `dynamic` configuration using an empty array in the provider.

After looking through the code I believe it has to do with the fact that every `connect` function also uses `init` in lib/config, which in turn is using a deep-copy of the previous session and only overwriting session properties that were set to some sort of "truthy" value (or not in reserved words .. e.g. "dynamic" is in there)

So my question really is .... is there any way to unset these lingering session values on connect, or is it considered best practice to unset them manually on callback?

Thanks for your help!
Eric

edit: Relevant code is:
* (request) https://github.com/simov/grant/blob/master/lib/request.js#L22
* (config) https://github.com/simov/grant/blob/master/lib/config.js#L185
* (init) https://github.com/simov/grant/blob/master/lib/config.js#L144