Spring Security Allow custom conversation for enum values in meta annotation expression templates

Arrays of enums in security meta annotations have limited utility because there's no clean mechanism to convert the enum to a custom value.

If I have an enum that specifies my permissions, such as:

enum Permission {
  READ("permission.read"),
  WRITE("permission.write");

  private final value;

  // constructor implementation

  @Override
  public String toString() {
    return value;
  }
}

I cannot have a working meta annotation with an array of enums such as the following:

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.TYPE, ElementType.METHOD })
@PreAuthorize("hasAnyAuthority({permissions})")
@interface HasAnyPermission {
 Permission[] permissions();
}

The ExpressionTemplateSecurityAnnotationScanner.conversionService includes EnumToStringConverter that will always use Enum.name() instead of my overridden toString() method.

Modifying the static conversionService initializer in ExpressionTemplateSecurityAnnotationScanner to:

static {
    conversionService.addConverter(new ClassToStringConverter());
    conversionService.removeConvertible(Enum.class, String.class);
}

corrects the issue.

Since the default Enum.toString() returns the enum's name, removing the explicit Enum converter would be backwards compatible for most code. I'm sure there's a more clever solution that ensures backwards compatibility.