Additional cookie configuration

[MaxGabriel]

I'd like to set the domain and same-site values of my cookies. That doesn't look possible with the current configuration, would you accept a pull request for it?

I could implement it just like the other cookie options—that's probably the easiest way. A more flexible option might be to let a user provide their own SetCookie to set arbitrary cookie values, but I thought you might be trying to avoid that.

[MaxGabriel]

Hm, after doing some investigation I think I'm going to need too many things different from serversession, so I'll probably just roll my own