private Challenge httpChallenge(final Authorization auth) {
        val challenge = locator.find(auth).orElseThrow();
        acmeChallengeRepository.add(challenge.getToken(), challenge.getAuthorization());
        return challenge;
    }
Prepares a HTTP challenge.
<p>
The verification of this challenge expects a file with a certain content to be
reachable at a given path under the domain to be tested.

@param auth {@link Authorization} to find the challenge in
@return {@link Challenge} to verify
support/cas-server-support-acme/src/main/java/org/apereo/cas/acme/DefaultAcmeCertificateManager.java