I know that you can create a project.json file to add NuGet packages to your functions, but how can I specify which channel I want to extract from them?
project.json
Azure features support the nuget.config standard approach for configuring custom sources. You can place the nuget.config file with your custom sources either in your functional folder or in the root directory of the application (where it will be used for all functions)
You can find more information about the file format and specify custom sources here: https://docs.nuget.org/consume/nuget-config-file#package-sources