Private VelaUX Authentication Configuration Fails due to UI Issuer URL Limitation

[oanasc]

Describe the bug
Authentication configuration with a private VelaUX not working with the options available in the UI configuration. We need a way to configure the Issuer URL

To Reproduce

1. Configure VelaUX:

   • Set VelaUX to be private and configured correctly.

2. Set up Dex:

   • Ensure Dex is publicly accessible and configured correctly

3. Configure Dex Connector:

   • Navigate to the dex connector in Vela UX and add a new connector of your choice

4. Enable SSO by Dex

   • Navigate to the Settings and choose the User login mode as SSO by dex

5. Issuer URL Configuration:

   • Observe that the Issuer URL is automatically derived from the velaAddress and stored in the dex-config secret.
   • Note that the default Issuer URL uses the private Vela URL.

6. Attempt Authentication:

   • Try to authenticate using the current configuration.
   • Notice that the authentication flow fails due to the private Issuer URL.

7. Workaround:

   • Manually set the Issuer URL in the dex-config secret to the public Dex URL.
   • Test authentication again and observe that it works with the manual configuration.

Expected behavior
We need a way to configure the Issuer URL. The dex-config gets updated on velaux restart and might override the workaround steps.

Screenshots

KubeVela Version
1.9.3

Additional context