diff --git a/example/server/storage/oidc.go b/example/server/storage/oidc.go
index 22c0295..c04877f 100644
--- a/example/server/storage/oidc.go
+++ b/example/server/storage/oidc.go
@@ -164,6 +164,15 @@ func authRequestToInternal(authReq *oidc.AuthRequest, userID string) *AuthReques
 	}
 }
 
+type AuthRequestWithSessionState struct {
+	*AuthRequest
+	SessionState string
+}
+
+func (a *AuthRequestWithSessionState) GetSessionState() string {
+	return a.SessionState
+}
+
 type OIDCCodeChallenge struct {
 	Challenge string
 	Method    string
diff --git a/pkg/oidc/error.go b/pkg/oidc/error.go
index 1100f73..d93cf44 100644
--- a/pkg/oidc/error.go
+++ b/pkg/oidc/error.go
@@ -133,6 +133,7 @@ type Error struct {
 	ErrorType        errorType `json:"error" schema:"error"`
 	Description      string    `json:"error_description,omitempty" schema:"error_description,omitempty"`
 	State            string    `json:"state,omitempty" schema:"state,omitempty"`
+	SessionState     string    `json:"session_state,omitempty" schema:"session_state,omitempty"`
 	redirectDisabled bool      `schema:"-"`
 	returnParent     bool      `schema:"-"`
 }
@@ -142,11 +143,13 @@ func (e *Error) MarshalJSON() ([]byte, error) {
 		Error            errorType `json:"error"`
 		ErrorDescription string    `json:"error_description,omitempty"`
 		State            string    `json:"state,omitempty"`
+		SessionState     string    `json:"session_state,omitempty"`
 		Parent           string    `json:"parent,omitempty"`
 	}{
 		Error:            e.ErrorType,
 		ErrorDescription: e.Description,
 		State:            e.State,
+		SessionState:     e.SessionState,
 	}
 	if e.returnParent {
 		m.Parent = e.Parent.Error()
@@ -176,7 +179,8 @@ func (e *Error) Is(target error) bool {
 	}
 	return e.ErrorType == t.ErrorType &&
 		(e.Description == t.Description || t.Description == "") &&
-		(e.State == t.State || t.State == "")
+		(e.State == t.State || t.State == "") &&
+		(e.SessionState == t.SessionState || t.SessionState == "")
 }
 
 func (e *Error) WithParent(err error) *Error {
@@ -242,6 +246,9 @@ func (e *Error) LogValue() slog.Value {
 	if e.State != "" {
 		attrs = append(attrs, slog.String("state", e.State))
 	}
+	if e.SessionState != "" {
+		attrs = append(attrs, slog.String("session_state", e.SessionState))
+	}
 	if e.redirectDisabled {
 		attrs = append(attrs, slog.Bool("redirect_disabled", e.redirectDisabled))
 	}
diff --git a/pkg/op/auth_request.go b/pkg/op/auth_request.go
index d6db62b..82f1b58 100644
--- a/pkg/op/auth_request.go
+++ b/pkg/op/auth_request.go
@@ -38,6 +38,13 @@ type AuthRequest interface {
 	Done() bool
 }
 
+// AuthRequestSessionState should be implemented if [OpenID Connect Session Management](https://openid.net/specs/openid-connect-session-1_0.html) is supported
+type AuthRequestSessionState interface {
+	// GetSessionState returns session_state.
+	// session_state is related to OpenID Connect Session Management.
+	GetSessionState() string
+}
+
 type Authorizer interface {
 	Storage() Storage
 	Decoder() httphelper.Decoder
@@ -103,8 +110,8 @@ func Authorize(w http.ResponseWriter, r *http.Request, authorizer Authorizer) {
 		}
 		return ValidateAuthRequestClient(ctx, authReq, client, verifier)
 	}
-	if validater, ok := authorizer.(AuthorizeValidator); ok {
-		validation = validater.ValidateAuthRequest
+	if validator, ok := authorizer.(AuthorizeValidator); ok {
+		validation = validator.ValidateAuthRequest
 	}
 	userID, err := validation(ctx, authReq, authorizer.Storage(), authorizer.IDTokenHintVerifier(ctx))
 	if err != nil {
@@ -481,12 +488,19 @@ func AuthResponseCode(w http.ResponseWriter, r *http.Request, authReq AuthReques
 		AuthRequestError(w, r, authReq, err, authorizer)
 		return
 	}
+	var sessionState string
+	authRequestSessionState, ok := authReq.(AuthRequestSessionState)
+	if ok {
+		sessionState = authRequestSessionState.GetSessionState()
+	}
 	codeResponse := struct {
-		Code  string `schema:"code"`
-		State string `schema:"state,omitempty"`
+		Code         string `schema:"code"`
+		State        string `schema:"state,omitempty"`
+		SessionState string `schema:"session_state,omitempty"`
 	}{
-		Code:  code,
-		State: authReq.GetState(),
+		Code:         code,
+		State:        authReq.GetState(),
+		SessionState: sessionState,
 	}
 
 	if authReq.GetResponseMode() == oidc.ResponseModeFormPost {
diff --git a/pkg/op/auth_request_test.go b/pkg/op/auth_request_test.go
index 765e602..4878f5e 100644
--- a/pkg/op/auth_request_test.go
+++ b/pkg/op/auth_request_test.go
@@ -1090,6 +1090,34 @@ func TestAuthResponseCode(t *testing.T) {
 				wantBody:           "",
 			},
 		},
+		{
+			name: "success with state and session_state",
+			args: args{
+				authReq: &storage.AuthRequestWithSessionState{
+					AuthRequest: &storage.AuthRequest{
+						ID:            "id1",
+						TransferState: "state1",
+					},
+					SessionState: "session_state1",
+				},
+				authorizer: func(t *testing.T) op.Authorizer {
+					ctrl := gomock.NewController(t)
+					storage := mock.NewMockStorage(ctrl)
+					storage.EXPECT().SaveAuthCode(gomock.Any(), "id1", "id1")
+
+					authorizer := mock.NewMockAuthorizer(ctrl)
+					authorizer.EXPECT().Storage().Return(storage)
+					authorizer.EXPECT().Crypto().Return(&mockCrypto{})
+					authorizer.EXPECT().Encoder().Return(schema.NewEncoder())
+					return authorizer
+				},
+			},
+			res: res{
+				wantCode:           http.StatusFound,
+				wantLocationHeader: "/auth/callback/?code=id1&session_state=session_state1&state=state1",
+				wantBody:           "",
+			},
+		},
 		{
 			name: "success without state", // reproduce issue #415
 			args: args{
diff --git a/pkg/op/config.go b/pkg/op/config.go
index 2fcede0..b271765 100644
--- a/pkg/op/config.go
+++ b/pkg/op/config.go
@@ -30,6 +30,7 @@ type Configuration interface {
 	EndSessionEndpoint() *Endpoint
 	KeysEndpoint() *Endpoint
 	DeviceAuthorizationEndpoint() *Endpoint
+	CheckSessionIframe() *Endpoint
 
 	AuthMethodPostSupported() bool
 	CodeMethodS256Supported() bool
diff --git a/pkg/op/discovery.go b/pkg/op/discovery.go
index e30a5a4..7aa7cf7 100644
--- a/pkg/op/discovery.go
+++ b/pkg/op/discovery.go
@@ -45,6 +45,7 @@ func CreateDiscoveryConfig(ctx context.Context, config Configuration, storage Di
 		EndSessionEndpoint:                         config.EndSessionEndpoint().Absolute(issuer),
 		JwksURI:                                    config.KeysEndpoint().Absolute(issuer),
 		DeviceAuthorizationEndpoint:                config.DeviceAuthorizationEndpoint().Absolute(issuer),
+		CheckSessionIframe:                         config.CheckSessionIframe().Absolute(issuer),
 		ScopesSupported:                            Scopes(config),
 		ResponseTypesSupported:                     ResponseTypes(config),
 		GrantTypesSupported:                        GrantTypes(config),
diff --git a/pkg/op/error.go b/pkg/op/error.go
index 44b1798..d57da83 100644
--- a/pkg/op/error.go
+++ b/pkg/op/error.go
@@ -46,6 +46,12 @@ func AuthRequestError(w http.ResponseWriter, r *http.Request, authReq ErrAuthReq
 		return
 	}
 	e.State = authReq.GetState()
+	var sessionState string
+	authRequestSessionState, ok := authReq.(AuthRequestSessionState)
+	if ok {
+		sessionState = authRequestSessionState.GetSessionState()
+	}
+	e.SessionState = sessionState
 	var responseMode oidc.ResponseMode
 	if rm, ok := authReq.(interface{ GetResponseMode() oidc.ResponseMode }); ok {
 		responseMode = rm.GetResponseMode()
@@ -92,6 +98,12 @@ func TryErrorRedirect(ctx context.Context, authReq ErrAuthRequest, parent error,
 	}
 
 	e.State = authReq.GetState()
+	var sessionState string
+	authRequestSessionState, ok := authReq.(AuthRequestSessionState)
+	if ok {
+		sessionState = authRequestSessionState.GetSessionState()
+	}
+	e.SessionState = sessionState
 	var responseMode oidc.ResponseMode
 	if rm, ok := authReq.(interface{ GetResponseMode() oidc.ResponseMode }); ok {
 		responseMode = rm.GetResponseMode()
diff --git a/pkg/op/mock/configuration.mock.go b/pkg/op/mock/configuration.mock.go
index 137c09d..0ef9d92 100644
--- a/pkg/op/mock/configuration.mock.go
+++ b/pkg/op/mock/configuration.mock.go
@@ -106,6 +106,20 @@ func (mr *MockConfigurationMockRecorder) BackChannelLogoutSupported() *gomock.Ca
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "BackChannelLogoutSupported", reflect.TypeOf((*MockConfiguration)(nil).BackChannelLogoutSupported))
 }
 
+// CheckSessionIframe mocks base method.
+func (m *MockConfiguration) CheckSessionIframe() *op.Endpoint {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "CheckSessionIframe")
+	ret0, _ := ret[0].(*op.Endpoint)
+	return ret0
+}
+
+// CheckSessionIframe indicates an expected call of CheckSessionIframe.
+func (mr *MockConfigurationMockRecorder) CheckSessionIframe() *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "CheckSessionIframe", reflect.TypeOf((*MockConfiguration)(nil).CheckSessionIframe))
+}
+
 // CodeMethodS256Supported mocks base method.
 func (m *MockConfiguration) CodeMethodS256Supported() bool {
 	m.ctrl.T.Helper()
diff --git a/pkg/op/op.go b/pkg/op/op.go
index 190c2c4..58ae838 100644
--- a/pkg/op/op.go
+++ b/pkg/op/op.go
@@ -339,6 +339,10 @@ func (o *Provider) DeviceAuthorizationEndpoint() *Endpoint {
 	return o.endpoints.DeviceAuthorization
 }
 
+func (o *Provider) CheckSessionIframe() *Endpoint {
+	return o.endpoints.CheckSessionIframe
+}
+
 func (o *Provider) KeysEndpoint() *Endpoint {
 	return o.endpoints.JwksURI
 }