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Create DropBox app: https://www.dropbox.com/developers/apps/create
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Create Google app: https://developers.google.com/ad-exchange/rtb/open-bidder/google-app-guide
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Create Yandex app: https://oauth.yandex.ru/client/new
After creating apps, specify your apps secret in yandex.c, google.c, test.c, cloud.c
MIT.