How to simulate/mock the passing of time for browser?

Problem:

• Trying to simulate/mock passing of time to reproduce a bug - a user is auto logged out after X amount of time which is not desired (our code has set session timeout already very long, thus this should not happen)

Solution needed:

• is there a way or tool to emulate passing of time from client (browser) side?
• we have control to the server and the code, so if your answer will need to adjust server/code, it's no problem for us as well

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Note: have already checked stackoverflow and googled around, but it seems the only way to emulate passing of time for this problem, is to direct adjust the time of the server, but I assume there is a better solution to this? ;)