Joshkunz Joshkunz - 26 days ago 8
HTTP Question

Correct way to delete cookies server-side

For my authentication process I use py-bcrypt to create a unique token when a user logs in and put that into a cookie which is used for authentication.

So I would send something like this from the server:

Set-Cookie: token=$2a$12$T94df7ArHkpkX7RGYndcq.fKU.oRlkVLOkCBNrMilaSWnTcWtCfJC; path=/;


Which works on all browsers. Then to delete a cookie I send a similar cookie with the
expires
field set for January 1st 1970

Set-Cookie: token=$2a$12$T94df7ArHkpkX7RGYndcq.fKU.oRlkVLOkCBNrMilaSWnTcWtCfJC; path=/; expires=Thu, Jan 01 1970 00:00:00 UTC;


And that works fine on Firefox but doesn't delete the cookie on IE or Safari.

So what is the best way to delete a cookie (without JavaScript preferably)? The set-the-expires-in-the-past method seems bulky. And also why does this work in FF but not in IE or Safari?

Answer

Sending the same cookie value with ; expires appended is a bad idea since you want the contents to be destroyed.

A better idea would be invalidating the cookie by setting the value to rubbish empty and include an expires field as well:

Set-Cookie: token=deleted; path=/; expires=Thu, 01 Jan 1970 00:00:00 GMT

Note that you cannot force all browsers to delete a cookie. The client can configure the browser in such a way that the cookie persists, even if it's expired. Setting the value as described above would solve this problem.