Need to pass current user in encoded format from Saas page using EL expression

Hi All,

We have a requirement where we need to call third party API from fusion ERP Page. As part of Parameter we need to pass the current user details. As of now We created the Sandbox and using system param we are able to pass current user name. But because of security reason Client wants to pass the user name in encoded format like 64 bit encoding or if we can replace the alphabets with respective numeric values using EL expression. We created a custom page using page integration. If anyone does this encoding or replacing the alphabet with number. Need