diff --git a/src/data/id_token.rs b/src/data/id_token.rs
index 72fb41f..e6f1697 100644
--- a/src/data/id_token.rs
+++ b/src/data/id_token.rs
@@ -25,8 +25,13 @@ pub struct IdToken {
     pub nonce: Option<String>,
 }
 
+#[derive(serde::Serialize, serde::Deserialize)]
+pub struct CustomIdTokenClaims {
+    auth_time: u64,
+}
+
 impl IdToken {
-    pub fn to_jwt_claims(self) -> JWTClaims<()> {
+    pub fn to_jwt_claims(self) -> JWTClaims<CustomIdTokenClaims> {
         JWTClaims {
             issued_at: Some(Duration::from_secs(self.issued_at)),
             expires_at: Some(Duration::from_secs(self.expiration_time)),
@@ -36,7 +41,9 @@ impl IdToken {
             audiences: Some(Audiences::AsString(self.audience)),
             jwt_id: None,
             nonce: self.nonce,
-            custom: (),
+            custom: CustomIdTokenClaims {
+                auth_time: self.auth_time
+            },
         }
     }
 }
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