Crowd uses apache.commons.validator to validate the URL in the Assertion Consumer Service field and if the domain name is not registered as a Top-level domain with IANA, the validation will fail to result in an invalid URL error.
As the crowd can be used internally, there is no guarantee that the domain name would be always registered so we need a way to let the customer override this.

Workaround
The current workaround is to manipulate this configuration from the database by updating cwd_application_saml_config.