The actual version of the switch node
(nodered 3.0.2) accepts, in "Edit switch node' pad, msg.|flow.|global.|string|number|Jexpression|env.variabile|previus value but not credentials.
I am in the (rare) situation of using IOT device IDs as values in a selector.
Throughout my flow the IDs (used as primary key) are always in credentials, especially to be able to export and exchange the flow safely. Except in the switch node.
Sincerely
m.s.