Cookie adapter does not use client secret passed in AuthHandlerParams or AppSessionCookieStoreFactoryParams

[dovca]

Describe the bug
Although clientSecret is a required property in AuthHandlerParams and is internally available, cookie adapter in createCookieAdapter still takes its own value from process.env['CLIENT_SECRET']. This is unusable, when the environment variable needs to have a different name or come from a different source.

To Reproduce
Steps to reproduce the behavior:

1. Leave the CLIENT_SECRET env variable undefined
2. Pass a clientSecret to getSessionStore as a constant string
3. Call getSessionStore
4. Session token fails to verify inside cookie adapter because process.env['CLIENT_SECRET'] is undefined

Expected behavior
The cookie adapter can take the client secret from the params passed to getSessionStore(params)

Additional context
Pull request will be provided.