Support SignalR scenarios with Blazor Server

[mkArtakMSFT]

For example, how to do pub/sub from a Blazor Server apps.

Be able to host a new hub on the server and simulate loopback connections between the hubs or provide some other mechanism to subscribe to SignalR invocations on the server efficiently.

[nwoolls]

If this is a new effort it would be nice if this method worked with Blazor auto render mode as well, so that the same code / experience can start with Blazor Server and then move to Blazor WASM once assets have been downloaded.

[njannink]

SignalR support for Blazor server (and auto) is really something I already trying to get to work officially for many years now.

All solutions are half-baked and smell like hacks. The propsed work-arounds using the CircuitHandler doesn't work in combination with Azure Frontdoor, because the HttpContext is somewhere else. The only thing that works in Net8 & Net9 with authenticated SignalR is passing the access_token down the line from the App.razor. Anywhere later in the pipeline the HttpContext is null when using Azure Frontdoor.

I don't exactly oversee all the possible issues with passing the access_token in the App.razor / _hosts.cshtml, some that I can think off:

• is this completely secure?
• token expiration/refresh flow support

A clear and clean worked out example of how to do this with an authenticated ChatHub and the various Blazor deployment options would be really appreciated.

[njannink]

Here one of my old defects/questions: #54134