dashboard: permissions for setting up SSO (#21837) (#21856)

Author: ti-chi-bot

dashboard/dashboard-session-sso.md

@@ -17,6 +17,10 @@ TiDB Dashboard supports [OIDC](https://openid.net/connect/)-based Single Sign-On
 
 3. In the **Single Sign-On** section, select **Enable to use SSO when sign into TiDB Dashboard**.
 
+    > **Note:**
+    >
+    > If your account does not have the `SYSTEM_VARIABLES_ADMIN` permission, the **Enable to use SSO when sign into TiDB Dashboard** option is disabled. For more information on permissions, see [TiDB Dashboard User Management](/dashboard/dashboard-user.md).
+
 4. Fill the **OIDC Client ID** and the **OIDC Discovery URL** fields in the form.
 
     Generally, you can obtain the two fields from the SSO service provider:
@@ -237,4 +241,4 @@ Now TiDB Dashboard has been configured to use Auth0 SSO for sign-in.
 
     ![Settings](/media/dashboard/dashboard-session-sso-casdoor-settings-3.png)
 
-Now TiDB Dashboard has been configured to use Casdoor SSO for sign-in.
+Now TiDB Dashboard has been configured to use Casdoor SSO for sign-in.