Clerk, the drop-in authentication and user management solution for React, today announced a $15 million Series A led by Madrona, with managing director Karan Mehandru joining its board. Mehandru brings a deep understanding of the space from his years on the board of Auth0. Other new investors include Vercel's CEO Guillermo Rauch, Mango Capital, and Auth0's former CRO Dave Wilner. Existing investors Andreessen Horowitz, S28 Capital, and Fathom Capital also participated.