♻️ refactor(auth): move UserContextKey from pkg/greet to pkg/auth

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

pkg/auth/context.go

@@ -0,0 +1,30 @@
+// Package auth — context keys and helpers for authentication state.
+//
+// This file owns the symbols that other packages use to read/write the
+// authenticated user from a request context. Previously these symbols
+// lived in pkg/greet/ which was the wrong home (auth concern in greet
+// package) ; moved here as part of the middleware design cleanup.
+package auth
+
+import (
+	"context"
+
+	"dance-lessons-coach/pkg/user"
+)
+
+// contextKey is unexported to prevent collisions with other packages
+// using string keys (Go convention).
+type contextKey string
+
+// UserContextKey is the key under which the authenticated user is
+// stored in the request context by AuthMiddleware.
+const UserContextKey contextKey = "authenticatedUser"
+
+// GetAuthenticatedUserFromContext extracts the authenticated user from
+// the request context. Returns (nil, false) if no user is present
+// (which is the case for unauthenticated requests AND for requests
+// that failed silent fail-through ; cf. AuthMiddleware semantics).
+func GetAuthenticatedUserFromContext(ctx context.Context) (*user.User, bool) {
+	u, ok := ctx.Value(UserContextKey).(*user.User)
+	return u, ok
+}