Values of authentication plugin properties are not resolvable as expressions. The model, however, indicates that they should be:

"plug-in" => {
"description" => "Configuration of a user store plug-in for use by the realm.",
"attributes" => { ... },
"operations" => undefined,
"children" => {"property" => {
...
"model-description" => {"*" => {
"description" => "A property within a security realm resource.",
"attributes" => {"value" => {
"type" => STRING,
"description" => "The optional value of the property.",
"expressions-allowed" => true,
"nillable" => true,
"min-length" => 1L,
"max-length" => 2147483647L,
"access-type" => "read-write",
"storage" => "configuration",
"restart-required" => "resource-services"
}},
"operations" => undefined,
"children" => {}
}}
}}
},

This indicates expressions are allowed. I do not believe that the plugin service ever actually resolves these expressions, though, so they are passed into the map as unresolved strings.

At that point, I don't believe that the plugin will have the ability to resolve them.