Support custom post_logout_redirect_uri

[ceefour]

Currently the post_logout_redirect_uri is always https://about.lovia.life/wp-login.php?loggedout=true&wp_lang=en_US, which is not always desirable, and may cause error because it's not an allowed post_logout URI, e.g. with FusionAuth:

Error

We're sorry, your request was malformed or was unable to be completed for some reason. Try hitting the back button and restarting the process to see if it fixes the problem.

If you want the nerdy explanation, review the following JSON body.
{
  "error" : "invalid_request",
  "error_description" : "The post_logout_redirect_uri is invalid.",
  "error_reason" : "invalid_post_logout_redirect_uri"
}

We should be able to customize the logout URI specifically, or just leave it empty (so the OIDC provider will determine where to go after logout).

Especially with SSO enabled, after logout should go back to home page, not to "login" page.

[bpetersen1]

This will be so helpful, I'm experiencing the same issue. If we could have a custom logout URI that would make life so much better.

[AdamTheRedBaron]

Hi folks, a great plugin that I have working very well for openID sso with WHMCS. The one issue I have is that users are left at the WHMCS url when logging out and I would ideally like them to be redirected to the original site homepage. Is there any workaround?

Keep up the great work!