The upgrade request
The negotiated subprotocol, when one was selected
Optionalprincipal: IPrincipal
The authenticated principal, when one authenticated the
upgrade. When absent the user key is omitted entirely rather than set to
undefined, keeping the context exactOptionalPropertyTypes-clean:
'user' in context is false for an anonymous connection.
The connection context
Builds the context handed to
onOpenfrom the upgrade request.