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How to add HTTP_PROVIDERS to an UpgradeProvider bootstrap in Angular 2?
I use:
let adapter: UpgradeAdapter = new UpgradeAdapter();
[...]
adapter.bootstrap(document.body, ["app"]);

To bootstap my Angular application. Now I need to add HTTP_PROVIDERS to this. I have tried many variations but none did work including:
adapter.bootstrap(document.body, ["app", HTTP_PROVIDERS]);

adapter.bootstrap(document.body, ["app", [HTTP_PROVIDERS]]);

Does anyone know the correct way?

You can try 
adapter.addProvider(HTTP_PROVIDERS); 

