Minimum spanning tree with required edge

You are laying fiber to connect n data centers (0..n-1). You are given a list of candidate edges [u, v, cost] and one required edge [u, v, cost] that policy forces you to build (e.g. a regulated backbone link). Return the minimum total cost to connect all n data centers into one network that includes the required edge, or -1 if full connectivity is impossible. The required edge may or may not appear in the candidate list.