Exposed UserAuthorization functionality via ITurnContext extensions

[tracyboehrer]

As a convenience, exposed UserAuthorization via ITurnContext extensions.

1. know what auth handlers are in use for this turnhandler
2. default "getturntoken" to get the first authhandler passed into the turn handler
3. support a mapping of connection to available auth handlers ( this is to support multiple routes requiring various auth handlers where the same executing logic is used for all routes )
4. fix a bug with auth handler resolution when provided with a connection handler and a scope ( this currently fails to resolve )

Summary

• ITurnContext.GetTurnTokenAsync
• ITurnContext.ExchangeTurnTokenAsync
• (NEW) ITurnContext.GetTurnTokens
  • Returns a dictionary of resolved tokens during the turn
• (BREAKING) When calling Get/Exchange without a handler name, the first resolved is used (not DefaultHandlerName).
  • This can be a bit confusing when AutoSignIn and Per-Route are used as the DefaultHandlerName used by Auto will always be first.

TBD

• support a mapping of connection to available auth handlers ( this is to support multiple routes requiring various auth handlers where the same executing logic is used for all routes )