Abstract: User authentication is a very important online environment issue. Further, investigation is needed to focus on improving user authentication methods for the sake of improving e-Learning security mechanisms; especially in the field of online exams. This study is the result of a systematic literature review which will answer the following three main questions of online exam user authentication methods, systems and threats. The results cover four main directions. First, it shows complete authentication methods that have been used in online exam systems; whether they are classified as knowledge, possession or biometric based. Second, it summarizes the online exam systems and authentication techniques used whether they are classified as user identification, authentication or continuous authentication. Third, it explores the threats that may occur during exam sessions and specifically classifies impersonation threats. Finally, it investigates existing commercial user authentication products that are used to observe online exams.