Unraveling the Cookie with cookie-parser

Question

Unraveling the Cookie with cookie-parser

I've been attempting to decode a cookie without much luck. The cookie looks like this:

s%3Ak0tBm_lnBeH4G5pPIbbFKktQl0l4pNU8.d2ZbSvwFjkmVWfcS9Wn0%2Fi2oSnTYI09krfOOWJAXirE

.

This particular cookie was generated using the express-session module.

My unsuccessful attempt at decoding the cookie involved the following code snippet:

const cookieParser = require("cookie-parser");
console.log(cookieParser.signedCookie("s%3Ak0tBm_lnBeH4G5pPIbbFKktQl0l4pNU8.d2ZbSvwFjkmVWfcS9Wn0%2Fi2oSnTYI09krfOOWJAXirE", "jksadhjk123io12ejnmlad'132hv8891"));

Instead of the expected decoded data, I only received the first parameter of signedCookie ("s%3Ak0tBm_..."). What I'm hoping for is something along the lines of:


{
   { path: '/',
     _expires: 2019-09-08T22:33:17.317Z,
     originalMaxAge: 3600000,
     httpOnly: true,
     secure: false,
     domain: null,
     sameSite: true
   },
   userID: 5d6ffe165d6eb10a7905c633
}

javascript express express-session

Answer 1

Answer №1

It appears that there was an issue validating the signature between the provided secret and the string. The correct syntax is as follows:

cookieParser.signedCookie(str, secret);

For more information, you can refer to this source, which explains that both,

If the value wasn't signed, it will return the original value.

and

If the value was signed but the signature couldn't be validated, it will return false.

Answer 2

It appears that there was an issue validating the signature between the provided secret and the string. The correct syntax is as follows:

cookieParser.signedCookie(str, secret);

For more information, you can refer to this source, which explains that both,

If the value wasn't signed, it will return the original value.

and

If the value was signed but the signature couldn't be validated, it will return false.

Answer 3

Answer №2

In summary: The cookie value needs to be decoded from URL encoding before using cookie-parser.

If you utilized express's res.cookie() method to set and sign the original cookie, you must also incorporate the second-party cookie-parser middleware, as outlined in express's documentation for res.cookie:

With the use of cookie-parser middleware and setting the signed option to true, res.cookie() will utilize the secret passed to cookieParser(secret) for signing the value.

Express appends a ":s" prefix to the signed cookies, as evident in the code snippet from express's response.js on GitHub:

if (signed) {
  val = 's:' + sign(val, secret);
}

It seems that your cookie value was initially encoded (express defaults to encodeURIComponent). The encoded form of ":s" is "%3s", hence your cookie value starting with s%3Ak0tBm...

Providing an encoded value to cookie-parser.signedCookie will not be effective, as shown by inspecting its code:

if (str.substr(0, 2) !== 's:') {
  return str
}

If cookie-parser serves as express middleware ahead of the concerned code, cookie values will be correctly decoded by the middleware and accessible via req.signedCookies. However, when using the signedCookie method sporadically, manual decoding such as decodeURIComponent will be necessary.

Additionally, consider exploring the encode option within res.cookie for a custom encoding solution.

Once a correctly decoded value is provided to cookie-parser, it will successfully parse your signed cookie value.

Answer 4

In summary: The cookie value needs to be decoded from URL encoding before using cookie-parser.

If you utilized express's res.cookie() method to set and sign the original cookie, you must also incorporate the second-party cookie-parser middleware, as outlined in express's documentation for res.cookie:

With the use of cookie-parser middleware and setting the signed option to true, res.cookie() will utilize the secret passed to cookieParser(secret) for signing the value.

Express appends a ":s" prefix to the signed cookies, as evident in the code snippet from express's response.js on GitHub:

if (signed) {
  val = 's:' + sign(val, secret);
}

It seems that your cookie value was initially encoded (express defaults to encodeURIComponent). The encoded form of ":s" is "%3s", hence your cookie value starting with s%3Ak0tBm...

Providing an encoded value to cookie-parser.signedCookie will not be effective, as shown by inspecting its code:

if (str.substr(0, 2) !== 's:') {
  return str
}

If cookie-parser serves as express middleware ahead of the concerned code, cookie values will be correctly decoded by the middleware and accessible via req.signedCookies. However, when using the signedCookie method sporadically, manual decoding such as decodeURIComponent will be necessary.

Additionally, consider exploring the encode option within res.cookie for a custom encoding solution.

Once a correctly decoded value is provided to cookie-parser, it will successfully parse your signed cookie value.

Unraveling the Cookie with cookie-parser

Answer №1

Answer №2

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