Need a mechanism to output binary expressions as hexadecimal strings

A prospective user attempted to use the following expression for a value of a Radius attribute:

{ "name": "Password" "expr": "pkt4.mac" }

The value produced by pkt4.mac, is a series of binary bytes, which cannot be expressed in a Radius authorization file. The radius server actually errors out stating the values do not match. We need a way to convert an expression result to a string literal such as:

"0xXXXXX" or "xx:xx:xx"

We could do it as perhaps a function:

hexString(pkt4.mac)

This would be useful beyond this particular case involving Radius. As an aside using the same expression for User Name or Connection Id work because we convert it to a string, under the covers.