Building Claudius: Auth, Role Resolution, and User Provisioning with Auth.js and MongoDB

Short summary

Third in a series on building Claudius, a Claude-based chatbot, this article covers the foundational infrastructure: identity system using Auth.js v5 with Google OAuth, server-side role resolution (admin/member/guest), and user provisioning via MongoDB. Roles are never client-supplied—always resolved server-side with JWT caching. The provisioning logic uses MongoDB aggregation pipelines with $ifNull to preserve admin changes while defaulting new fields.

• •Auth.js v5 with Google OAuth and MongoDB adapter for secure sign-in
• •Server-side role resolution prevents client-side privilege escalation
• •User provisioning uses MongoDB aggregation pipelines with $ifNull for safe defaults

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