fix: primary keys are implicitly uniquely constrained.

Closes #332.

lib/ash_authentication/validations/attribute.ex

@@ -60,8 +60,25 @@ defmodule AshAuthentication.Validations.Attribute do
   """
   @spec validate_attribute_unique_constraint(map, [atom], module) :: :ok | {:error, Exception.t()}
   def validate_attribute_unique_constraint(dsl_state, fields, resource) do
+    fields = MapSet.new(fields)
+
+    identities =
+      dsl_state
+      |> Info.identities()
+      |> Enum.map(&MapSet.new(&1.keys))
+
+    primary_key =
+      dsl_state
+      |> Info.primary_key()
+      |> MapSet.new()
+
+    identities
+    |> Enum.concat(primary_key)
+    |> Enum.find(&MapSet.equal?(&1, fields))
+    |> case do
+      nil ->
         message =
-      case fields do
+          case Enum.to_list(fields) do
             [field] ->
               "The `#{inspect(field)}` attribute on the resource `#{inspect(resource)}` should be uniquely constrained"
 
@@ -74,14 +91,10 @@ defmodule AshAuthentication.Validations.Attribute do
               "The #{fields} attributes on the resource `#{inspect(resource)}` should be uniquely constrained"
           end
 
-    fields = MapSet.new(fields)
+        {:error, DslError.exception(path: [:identities, :identity], message: message)}
 
-    dsl_state
+      _ ->
-    |> Info.identities()
+        :ok
-    |> Enum.find(&MapSet.equal?(MapSet.new(&1.keys), fields))
-    |> case do
-      nil -> {:error, DslError.exception(path: [:identities, :identity], message: message)}
-      _ -> :ok
     end
   end
 end