Access Token is the globally unique interface call credential of BesChannels OpenAPI, and the token is required when calling each interface. Developers need to properly save. The storage of access_token must reserve at least 512 characters. The validity period of access_token is currently 2 hours and needs to be refreshed regularly. During this period, if it is generated again, if the remaining time of the token exceeds 20 minutes, the original token will still be returned, and the remaining time will be updated to the actual remaining time. If the remaining time of the original token is less than 20 minutes, a new one will be generated to replace the old one , and the update is 2 hours. If the old one is still valid after the update, it can still be used normally. That is to say, when the remaining time is less than 20 minutes, there may be two available tokens at the same time