Answer
ArgoCD ships two built-in roles: role:admin (full access to everything) and role:readonly (view-only). You define custom roles in the RBAC policy for finer control. The policy.default sets the fallback role for users without a specific grant (often readonly or empty to deny).
policy.default: role:readonlyReal-world example Unmapped users default to readonly, while a custom 'team-a' role grants sync rights on team-a apps only.