Just a note to self and anyone who will have the same issue.

It seems like only relative to server address redirect URLs are supported via default Hawkular configuration [1]. I. e. OAuth redirect to "http://localhost/oauth-callback" will not work, only "http://hawkular-server-address.link/oauth-callback" will do the trick. I was confused for a while because all AeroGear examples set it to "http://localhost" and that’s it.

[1]: https://github.com/hawkular/hawkular-accounts/blob/70e6db131368248d0e586f9b28b7a4eb71a18b64/dist/src/main/resources/standalone/configuration/hawkular-realm.json#L98