Provide support for custom authorization servers in Okta

Decided to keep the config simple and just allow a plain textfield rather than options for org / default / other.

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With this modification, the validation function checks if the authorization_server field is non-empty before checking whether it contains a / character. If the field is non-empty and contains a /, an error is set indicating that it cannot contain a slash. This ensures that the server ID, if provided, does not contain a /.

Please don't create a new merge request. You can commit on top of the existing merge request.

jcnventura → closed merge request !106