Decrypt a Cookie

There is a function to validate a JWT token passed in the QueryString, but is there a way to decrypt a cookie as well?

What I am attempting to do is decrypt a cookie, check the information for the user in said cookie and add a header that identifies the user as authenticated.

The function would then add a header to the request identifying the user as such. This would allow us to serve protected content cached at CloudFront as opposed to going deeper into our stack.