https://msdn.microsoft.com/library/jj950082.aspx tem o seguinte código.

void IterateJSONValue()
{
    // Create a JSON object.
    json::value obj;
    obj[L"key1"] = json::value::boolean(false);
    obj[L"key2"] = json::value::number(44);
    obj[L"key3"] = json::value::number(43.6);
    obj[L"key4"] = json::value::string(U("str"));

    // Loop over each element in the object.
    for(auto iter = obj.cbegin(); iter != obj.cend(); ++iter)
    {
        // Make sure to get the value as const reference otherwise you will end up copying
        // the whole JSON value recursively which can be expensive if it is a nested object.
        const json::value &str = iter->first;
        const json::value &v = iter->second;

        // Perform actions here to process each string and value in the JSON object...
        std::wcout << L"String: " << str.as_string() << L", Value: " << v.to_string() << endl;
    }

    /* Output:
    String: key1, Value: false
    String: key2, Value: 44
    String: key3, Value: 43.6
    String: key4, Value: str
    */
}

No entanto, com o C ++ REST SDK 2.6.0, parece que não há método cbegin no json :: value. Sem ele, qual seria a maneira correta de iterar através da chave: valores de um nó json (valor)?