When Apache Syncope is configured to work in HTTPS, export (thus download) of documents as content.xml or reports (all available formats) fails returning HttpClientProtocol exception and message "the server failed to respond with a valid HTTP response".
To reproduce the error:
1. Setup Apache Syncope to work over HTTPS connection (edit console configuration.properties).
2. Deploy and run on a web server (Apache Tomcat for example).
4. Log-in with credentials admin, password.
3. Try to export Content (Configuration > DB export).