test: Add tests for iat claim

Author: jonasroussel

test/header_test.dart

@@ -25,11 +25,11 @@ void main() {
       });
 
       test('should be still valid', () {
-        final iat = DateTime(2023);
-        final exp = DateTime(2023).add(Duration(hours: 1));
+        final iat = DateTime(2042);
+        final exp = DateTime(2042).add(Duration(hours: 1));
 
         withClock(
-          Clock.fixed(DateTime(2023)),
+          Clock.fixed(DateTime(2042)),
           () {
             final duration = Duration(hours: 1);
             final token = JWT({'foo': 'bar'}).sign(hsKey, expiresIn: duration);
@@ -61,7 +61,7 @@ void main() {
     });
 
     //----------------------//
-    //  Not Before (nbf)   //
+    //   Not Before (nbf)   //
     //----------------------//
     group('nbf', () {
       test('should throw when token is not yet valid', () {
@@ -75,11 +75,11 @@ void main() {
       });
 
       test('should be valid after nbf time', () {
-        final iat = DateTime(2023);
+        final iat = DateTime(2042);
         final nbf = iat.add(Duration(minutes: 30));
 
         withClock(
-          Clock.fixed(DateTime(2023)),
+          Clock.fixed(DateTime(2042)),
           () {
             final token = JWT({'foo': 'bar'}).sign(
               hsKey,
@@ -112,6 +112,40 @@ void main() {
           contains('foo'),
         );
       });
+
+      //----------------------//
+      //   Issued At (iat)   //
+      //----------------------//
+      group('iat', () {
+        test('should have iat claim by default', () {
+          final iat = DateTime(2042);
+
+          withClock(Clock.fixed(iat), () {
+            final token = JWT({'foo': 'bar'}).sign(hsKey);
+
+            expect(
+              JWT.verify(token, hsKey).payload,
+              equals({
+                'foo': 'bar',
+                'iat': iat.millisecondsSinceEpoch ~/ 1000,
+              }),
+            );
+          });
+        });
+
+        test('should be valid when iat is in the future', () {
+          final futureIat = DateTime(2042).add(Duration(hours: 1));
+          final token = JWT({
+            'foo': 'bar',
+            'iat': futureIat.millisecondsSinceEpoch ~/ 1000
+          }).sign(hsKey);
+
+          expect(
+            JWT.verify(token, hsKey).payload,
+            contains('foo'),
+          );
+        });
+      });
     });
   });
 }