The parameter HubConnectionContext context is different between the ASP.NET Core SignalR SDK and the Azure SignalR Service SDK when IUserIdProvider is called.
In ASP.NET Core SignalR, HubConnectionContext context is the context from the physical client connection with valid values for all properties.
In the Azure SignalR Service SDK, HubConnectionContext context is the context from the logical client connection. The physical client is connected to the Azure SignalR Service instance, so only a limited number of properties are provided.
For now, only HubConnectionContext.GetHttpContext() and HubConnectionContext.User are available for access.
You can check the source code.