diff --git a/app/controllers/concerns/authentication.rb b/app/controllers/concerns/authentication.rb
index b1e4bbd..542db5f 100644
--- a/app/controllers/concerns/authentication.rb
+++ b/app/controllers/concerns/authentication.rb
@@ -49,9 +49,6 @@ module Authentication
       user.sessions.create!(user_agent: request.user_agent, ip_address: request.remote_ip).tap do |session|
         Current.session = session
 
-        # Store auth_time in session for OIDC max_age support
-        session[:auth_time] = Time.now.to_i
-
         # Extract root domain for cross-subdomain cookies (required for forward auth)
         domain = extract_root_domain(request.host)
 
diff --git a/app/controllers/oidc_controller.rb b/app/controllers/oidc_controller.rb
index aa1dff5..e93578f 100644
--- a/app/controllers/oidc_controller.rb
+++ b/app/controllers/oidc_controller.rb
@@ -412,13 +412,14 @@ class OidcController < ApplicationController
         end
 
         # Generate ID token (JWT) with pairwise SID, at_hash, and auth_time
+        # auth_time comes from the Session model's created_at (when user logged in)
         id_token = OidcJwtService.generate_id_token(
           user,
           application,
           consent: consent,
           nonce: auth_code.nonce,
           access_token: access_token_record.plaintext_token,
-          auth_time: session[:auth_time]
+          auth_time: Current.session.created_at.to_i
         )
 
         # Return tokens
@@ -536,12 +537,13 @@ class OidcController < ApplicationController
     end
 
     # Generate new ID token (JWT with pairwise SID, at_hash, and auth_time; no nonce for refresh grants)
+    # auth_time comes from the Session model's created_at (when user logged in)
     id_token = OidcJwtService.generate_id_token(
       user,
       application,
       consent: consent,
       access_token: new_access_token.plaintext_token,
-      auth_time: session[:auth_time]
+      auth_time: Current.session.created_at.to_i
     )
 
     # Return new tokens
diff --git a/test/controllers/oidc_pkce_controller_test.rb b/test/controllers/oidc_pkce_controller_test.rb
index 80acb05..ba4502e 100644
--- a/test/controllers/oidc_pkce_controller_test.rb
+++ b/test/controllers/oidc_pkce_controller_test.rb
@@ -532,7 +532,7 @@ class OidcPkceControllerTest < ActionDispatch::IntegrationTest
   # AUTH_TIME CLAIM TESTS
   # ====================
 
-  test "ID token includes auth_time claim from session" do
+  test "ID token includes auth_time claim from session created_at" do
     # Create consent
     OidcUserConsent.create!(
       user: @user,
@@ -548,8 +548,8 @@ class OidcPkceControllerTest < ActionDispatch::IntegrationTest
       .tr("+/", "-_")
       .tr("=", "")
 
-    # Set auth_time in session (simulating user login)
-    session[:auth_time] = Time.now.to_i - 300  # 5 minutes ago
+    # Get the expected auth_time from the session's created_at
+    expected_auth_time = Current.session.created_at.to_i
 
     # Create authorization code
     auth_code = OidcAuthorizationCode.create!(
@@ -577,10 +577,10 @@ class OidcPkceControllerTest < ActionDispatch::IntegrationTest
     tokens = JSON.parse(@response.body)
     assert tokens.key?("id_token")
 
-    # Decode and verify auth_time is present
+    # Decode and verify auth_time is present and matches session created_at
     decoded = JWT.decode(tokens["id_token"], nil, false).first
     assert_includes decoded.keys, "auth_time", "ID token should include auth_time"
-    assert_equal session[:auth_time], decoded["auth_time"], "auth_time should match session value"
+    assert_equal expected_auth_time, decoded["auth_time"], "auth_time should match session created_at"
   end
 
   test "ID token includes auth_time in refresh token flow" do
@@ -593,8 +593,8 @@ class OidcPkceControllerTest < ActionDispatch::IntegrationTest
       sid: "test-sid-refresh-auth-time"
     )
 
-    # Set auth_time in session
-    session[:auth_time] = Time.now.to_i - 600  # 10 minutes ago
+    # Get the expected auth_time from the session's created_at
+    expected_auth_time = Current.session.created_at.to_i
 
     # Create initial access and refresh tokens (bypass PKCE for this test)
     auth_code = OidcAuthorizationCode.create!(
@@ -638,10 +638,10 @@ class OidcPkceControllerTest < ActionDispatch::IntegrationTest
     new_tokens = JSON.parse(@response.body)
     assert new_tokens.key?("id_token")
 
-    # Decode and verify auth_time is still present from refresh
+    # Decode and verify auth_time is still present from session created_at
     decoded = JWT.decode(new_tokens["id_token"], nil, false).first
     assert_includes decoded.keys, "auth_time", "Refreshed ID token should include auth_time"
-    assert_equal session[:auth_time], decoded["auth_time"], "auth_time should persist from original session"
+    assert_equal expected_auth_time, decoded["auth_time"], "auth_time should match session created_at"
   end
 
   test "at_hash is correctly computed and included in ID token" do