feat: support for session_state (#712)

* add default signature algorithm

* implements session_state in auth_request.go

* add test

* Update pkg/op/auth_request.go

link to the standard

Co-authored-by: Tim Möhlmann <muhlemmer@gmail.com>

* add check_session_iframe

---------

Co-authored-by: Tim Möhlmann <tim+github@zitadel.com>
Co-authored-by: Tim Möhlmann <muhlemmer@gmail.com>

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