How to tell if a cookie has expired or has not yet been created

How to tell if a cookie has expired or has not yet been created
Now you want to integrate with a third-party system and share it through cookies!
Now do synchronous logoff!
That is, our system determines the state of the third-party system cookie value to execute a statement!
If a cookie is found to expire, execute statement 1 and EXECUTE statement 2 if the cookie is found not yet created!
Do not know how to do, please advise, thank you

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1. The premise is that two systems that need to be integrated must be under the same domain name
2. No difference from normal cookie operation
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1. The premise is that two systems that need to be integrated must be under the same domain name
2. No difference from normal cookie operation

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The first step: all verification must read the cookie, and then further verification

The second step: synchronous logout, in one place to log off the cookie, other places to verify the cookie does not exist, it is considered not logged in!
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Created at the same time, at the same time to be registered, through the same interface to do

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