From 7f6d323ddef87cef569b116d8c7ad1de044baf62 Mon Sep 17 00:00:00 2001
From: ybelMekk <youssef.bel.mekki@nav.no>
Date: Sat, 22 Jan 2022 16:23:16 +0100
Subject: [PATCH] add: session management check to get `session_state` from OP
 response, generate a externalSessionID if none supported.

---
 pkg/openid/configuration.go    |  9 +++++++++
 pkg/openid/token.go            | 12 ++++++------
 pkg/router/handler_callback.go | 24 ++++++++++++++++++++----
 3 files changed, 35 insertions(+), 10 deletions(-)

diff --git a/pkg/openid/configuration.go b/pkg/openid/configuration.go
index 8548327..24a2138 100644
--- a/pkg/openid/configuration.go
+++ b/pkg/openid/configuration.go
@@ -33,6 +33,7 @@ type Configuration struct {
 	RequestParameterSupported              bool      `json:"request_parameter_supported"`
 	RequestURIParameterSupported           bool      `json:"request_uri_parameter_supported"`
 	RequestObjectSigningAlgValuesSupported []string  `json:"request_object_signing_alg_values_supported"`
+	CheckSessionIframe                     string    `json:"check_session_iframe,omitempty"`
 }
 
 type Supported []string
@@ -71,3 +72,11 @@ func (c *Configuration) FetchJwkSet(ctx context.Context) (*jwk.Set, error) {
 
 	return &jwkSet, nil
 }
+
+func (c *Configuration) FetchCheckSessionIframe() bool {
+	if c.CheckSessionIframe == "" {
+		return false
+	}
+
+	return true
+}
diff --git a/pkg/openid/token.go b/pkg/openid/token.go
index 67c8629..020a859 100644
--- a/pkg/openid/token.go
+++ b/pkg/openid/token.go
@@ -22,18 +22,18 @@ func (in *IDToken) Validate(opts ...jwt.ValidateOption) error {
 	return nil
 }
 
-func (in *IDToken) GetSID() (string, error) {
-	sid, ok := in.Token.Get("sid")
+func (in *IDToken) GetStringClaim(claim string) (string, error) {
+	gotClaim, ok := in.Token.Get(claim)
 	if !ok {
-		return "", fmt.Errorf("missing required 'sid' claim in id_token")
+		return "", fmt.Errorf("missing required '%s' claim in id_token", claim)
 	}
 
-	sidString, ok := sid.(string)
+	claimString, ok := gotClaim.(string)
 	if !ok {
-		return "", fmt.Errorf("'sid' claim is not a string")
+		return "", fmt.Errorf("'%s' claim is not a string", claim)
 	}
 
-	return sidString, nil
+	return claimString, nil
 }
 
 func ParseIDToken(jwks jwk.Set, token *oauth2.Token) (*IDToken, error) {
diff --git a/pkg/router/handler_callback.go b/pkg/router/handler_callback.go
index 623c12a..92c3559 100644
--- a/pkg/router/handler_callback.go
+++ b/pkg/router/handler_callback.go
@@ -3,6 +3,7 @@ package router
 import (
 	"context"
 	"fmt"
+	"github.com/google/uuid"
 	"net/http"
 	"time"
 
@@ -82,6 +83,11 @@ func (h *Handler) codeExchangeForToken(ctx context.Context, loginCookie *openid.
 	return tokens, nil
 }
 
+func (h *Handler) sidClaimRequired() bool {
+	config := h.Provider.GetOpenIDConfiguration()
+	return config.FrontchannelLogoutSupported && config.FrontchannelLogoutSessionSupported
+}
+
 func (h *Handler) validateIDToken(idToken *openid.IDToken, loginCookie *openid.LoginCookie) (string, error) {
 	validateOpts := []jwt.ValidateOption{
 		jwt.WithAudience(h.Provider.GetClientConfiguration().GetClientID()),
@@ -103,7 +109,18 @@ func (h *Handler) validateIDToken(idToken *openid.IDToken, loginCookie *openid.L
 		return "", err
 	}
 
-	externalSessionID, err := idToken.GetSID()
+	var externalSessionID string
+
+	switch true {
+	case h.sidClaimRequired():
+		externalSessionID, err = idToken.GetStringClaim("sid")
+	case h.Provider.GetOpenIDConfiguration().FetchCheckSessionIframe():
+		externalSessionID, err = idToken.GetStringClaim("session_state")
+	default:
+		// generate external sid
+		externalSessionID = h.GenerateExternalSessionID()
+	}
+
 	if err != nil {
 		return "", fmt.Errorf("getting external session ID from id_token: %w", err)
 	}
@@ -111,7 +128,6 @@ func (h *Handler) validateIDToken(idToken *openid.IDToken, loginCookie *openid.L
 	return externalSessionID, nil
 }
 
-func (h *Handler) sidClaimRequired() bool {
-	config := h.Provider.GetOpenIDConfiguration()
-	return config.FrontchannelLogoutSupported && config.FrontchannelLogoutSessionSupported
+func (h *Handler) GenerateExternalSessionID() string {
+	return fmt.Sprintf("%s:%s:%s", h.Config.OpenID.Provider, h.Provider.GetClientConfiguration().GetClientID(), uuid.New().String())
 }