TextKey's JAVA library allows you to use REST API calls server-side from a Java backend. TextKey is an omni-factor authentication API that uses seven-factors of authentication to provide security for devices ranging from mobile to electronic door locks. TextKey works through using SMS service, unique code, cellular number, UDID, a single use URL, and an optional pin. TextKey uses Rest with a JSON response and SOAP. TextKey is free for ten users, and available for a monthly charge per user thereafter.