This study examines how authentic assessment could nurture students' epistemic agency: their sense of agency in using, evaluating and producing knowledge. Authentic assessment commonly emphasises 'realism' and 'employability skills'. As important as these ideas are, this approach to authentic assessment neglects the key academic value of "knowledge," a gap we address by adding epistemology into the conversation. Our qualitative case study explores an archaeology course whose authentic assessment design relied heavily on digital technologies. We empirically analyse students' sense of epistemic agency after articulating the affordances of the course's authentic assessment design. Our findings show that digitally-mediated authentic assessment promoted students' relationship with knowledge in three ways. Students understood themselves as (i) active learners, (ii) active users of knowledge and (iii) epistemic agents who contributed to public archaeological knowledge. We reframe authentic assessment as a catalyst for students' epistemic agency, enabling students to contribute to social good.