feat(shared): add EnsureCoreIndexes

shared/indexes/indexes.go

@@ -0,0 +1,39 @@
+// Package indexes declares the MongoDB indexes more than one Vantage service
+// depends on.
+package indexes
+
+import (
+	"context"
+	"fmt"
+
+	"go.mongodb.org/mongo-driver/v2/bson"
+	"go.mongodb.org/mongo-driver/v2/mongo"
+	"go.mongodb.org/mongo-driver/v2/mongo/options"
+)
+
+// EnsureCoreIndexes declares the unique indexes on users.email and orgs.slug.
+//
+// These are a security property, not an optimisation. GetUserByEmail does an
+// unscoped FindOne, so a duplicate email would let the OIDC cross-org guard
+// compare against an arbitrary user. Every caller must treat a failure here as
+// fatal.
+//
+// Creating an index that already exists with the same specification is a no-op,
+// so this is safe to call at every boot from every service.
+func EnsureCoreIndexes(ctx context.Context, db *mongo.Database) error {
+	if _, err := db.Collection("users").Indexes().CreateOne(ctx, mongo.IndexModel{
+		Keys:    bson.D{{Key: "email", Value: 1}},
+		Options: options.Index().SetUnique(true),
+	}); err != nil {
+		return fmt.Errorf("users.email index: %w", err)
+	}
+
+	if _, err := db.Collection("orgs").Indexes().CreateOne(ctx, mongo.IndexModel{
+		Keys:    bson.D{{Key: "slug", Value: 1}},
+		Options: options.Index().SetUnique(true),
+	}); err != nil {
+		return fmt.Errorf("orgs.slug index: %w", err)
+	}
+
+	return nil
+}