Add logic to handle both forms of id filter types that can be encounted

Include a test for the single ID JWT variable

graphql/resolve/auth_query_test.yaml

@@ -2127,3 +2127,27 @@
         Person.id : uid
       }
     }
+
+-
+  name: "Query auth rules with filter on field with ID type, single JWT ID param"
+  gqlquery: |
+    query{
+      queryPerson{
+        id
+        name
+      }
+    }
+  jwtvar:
+    USER: "0x5"
+  dgquery: |-
+    query {
+      queryPerson(func: uid(PersonRoot)) {
+        Person.id : uid
+        Person.name : Person.name
+      }
+      PersonRoot as var(func: uid(Person_1)) @filter(uid(Person_Auth2))
+      Person_1 as var(func: type(Person))
+      Person_Auth2 as var(func: uid(0x5)) @filter(type(Person)) @cascade {
+        Person.id : uid
+      }
+    }

graphql/resolve/query_rewriter.go

@@ -1573,7 +1573,18 @@ func idFilter(filter map[string]interface{}, idField schema.FieldDefinition) []u
 	if idsFilter == nil {
 		return nil
 	}
-	idsSlice := idsFilter.([]interface{})
+	var idsSlice []interface{}
+	// idsFilter can be an single string value (most common) or
+	// an interface{} slice
+	switch idsFilter.(type) {
+	case string:
+		idsSlice = append(idsSlice, idsFilter)
+	case []interface{}:
+		idsSlice = idsFilter.([]interface{})
+	default:
+		// if an unexpected type is encountered, fail silently
+		return nil
+	}
 	return convertIDs(idsSlice)
 }