How to configure http proxy settings?

When running func.exe from Visual Studio 2017 behind a firewall, the SignalR binding is not able to connect to the Azure SignalR service. What do we need to configure?

Exception:

```
[6-12-2018 14:09:42] Executed 'SendSignalRMessage' (Failed, Id=8d574364-87ff-489f-896f-fefafa7e47a3)
[6-12-2018 14:09:42] System.Private.CoreLib: Exception while executing function: SendSignalRMessage. System.Private.CoreLib: One or more errors occurred. (A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond). System.Net.Http: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond. System.Private.CoreLib: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
```

Package `Microsoft.Azure.WebJobs.Extensions.SignalRService` version `1.0.0-preview1-10025`.

Also raised a question on StackOverflow: https://stackoverflow.com/questions/53665556/signalr-binding-how-to-configure-http-proxy-settings-during-development-within

Start with the func.exe development scenario and the Microsoft.Azure.WebJobs.Extensions.SignalRService version named in the report. Determine whether proxy configuration is supported for this connection path; done means documenting the required setting or clearly recording that the issue needs a product change.

Written by the indexing model from the issue text.