What is the problem when using Flask login with multiple users and sharing the same session?

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When using Flask login with multiple users and sharing the same session, there is a risk of user data being overwritten or mixed up. As each user's information is stored in the session cookie, if two users log in from the same browser, their sessions may overlap or overwrite each other, leading to unexpected behavior and security vulnerabilities. Additionally, if one user logs out and the session is not properly cleared, the next user to log in could potentially gain access to the previous user's data. This can lead to confidentiality breaches and other security issues. Therefore, it is recommended to use separate sessions for each user to ensure user data is properly isolated and secured.