After successfully using Single Sign On, you may run into an issue if the server's certificate is renewed, with an error similar to the following:
Unable to obtain configuration from: 'System.string'.
Unable to retrieve document from: 'System.string'.
An error occurred while sending the request.
The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.
The remote certificate is invalid according to the validation procedure.
Try Validating again to accept this new Thumbprint.
You have been logged out.

If you are able to log back in to Wasp, you can try going into the SSO settings to verify everything is still correct and click Validate again. You should also check in your server's Proxy Configuration and make sure it is updated to use the new certificate.