Artifactory can be configured to allow anonymous access by ticking the Allow Anonymous Access checkbox, which can be found, in Artifactory 7.x, by navigating to Administration > Security > Settings (In Artifactory 6.x and under, by navigating to the Admin > Security > Security Configuration). Permissions granted under Artifactory’s Anonymous User category are configured and managed in the same way as are permission targets for any other user. If you've configured Artifactory for use by anonymous users, then whenever a non-authenticated user tries to access Artifactory content, those requests will be handled according to the permissions you've granted to your anonymous user.
If you'd prefer to not grant access to non-authenticated users, untick the Allow Anonymous Access checkbox and all such interactions will be disallowed.