Metadata on the connection

At this moment a connection (ConnectionContext) consists of a UserId only. For scenarios I have in mind, it should be possible to add some metadata or additional context to the connection at the point of creation.

var clientUri = _client.GetClientAccessUri("John", keyvaluepair);

on the server side we then should be able to get this information by getting it from the connection context again.

Start by tracing ConnectionContext and GetClientAccessUri in the client and server APIs. Determine how metadata supplied at connection creation should be represented and retrieved from the connection context. Done means a caller can provide key-value metadata when creating the connection and the server can read it back.

Written by the indexing model from the issue text.