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Ask HN: How to recognize web logins from new devices?

1 points by scrpn ↗ HN
For my project I want to notify the users by email in case there is a new login from a new device i.e. web browser. How are Google/Twitter/Facebook doing this? Is there a technical article describing this?

4 comments

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phillipseamore
What I've done in the past is to have an identifier in a cookie or localStorage that isn't cleared on logout. A new device would be one that doesn't have that identifier.
scrpn
what you put in that cookie and how did you matched on server side? could you share some pointers?
phillipseamore
For something really basic a simple hash like "username+my_secret" does the trick and is easy to check with nothing stored on the server side. I however have always created a uuid for each new device login and store in DB so the user can see a list of all devices used to login.