TL; DR
Is there any way you might suggest decrypting this cookie? It was saved under the name mail, so I suspect it encrypts an email address:
4520382156EFC790B5B54696C4E175B5695F03D2D59C33858A62D6CDA18B7AB2
Edit: Here is another one using another account:
BFE069DB7B7FDED51A7F81DF8CE3CAD8FB8B14D70BE3FA32F26C4A2136170CD6
Motivation
When using a web portal, I noticed the same cookie is generated for my username every single time (i.e., it does not appear to be random). My concern is that there are several API endpoints with private info that can be accessed anonymously just using said string in the URL. I suspect the string is a kind of user identifier, but I am not sure if it is generated using the values from my email address, or randomly based on time of creation.
More details
I can't go into specifics as I don't want this flaw to be exposed, compromising my info and getting me into trouble. However I know the portal is hosted on Microsoft IIS Server and built using the ASP.NET framework. I also suspect the implementation is rudimentary, so they probably aren't doing anything more sophisticated.