"default" access_token used by PHP SDK

When there is no active user session Facebook PHP SDK uses appid|appsecret string as access_token

Is this exact special kind of token described somewhere in开发者_JS百科 documentation?

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A token that contains appId|appSecret is the Application Access token.

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I know this question is specifically about the PHP SDK, but is there an equivalent for the JS SDK? I wondering how I could seamlessly integrate the fallback to Application Token when there is no logged in Facebook user with the JS SDK.