server: implement authentication

server/api/user.go

@@ -1,6 +1,7 @@
 package api
 
 import (
+	"context"
 	"errors"
 	"log/slog"
 	"net/http"
@@ -18,6 +19,33 @@ func Whoami(w http.ResponseWriter, r *http.Request) {
 		w.Write([]byte("anonymous"))
 		return
 	}
+
+	slog.Debug("user: returning username", "userid", user.ID, "username", user.Name)
+	w.Write([]byte(user.Name))
+}
+
+func LoginCtx(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		slog.Debug("user: entering LoginCtx middleware")
+		userID, ok := r.Context().Value(userIDKey).(uuid.UUID)
+		if !ok || userID == uuid.Nil {
+			slog.Debug("user: no user ID provided, assuming anonymous user")
+			next.ServeHTTP(w, r)
+			return
+		}
+
+		slog.Debug("user: fetching user by ID", "user ID", userID)
+		user, err := dbGetUser(userID.String())
+		if err != nil {
+			slog.Error("user: failed to fetch user by ID", "user ID", userID, "error", err)
+			render.Render(w, r, ErrNotFound)
+			return
+		}
+
+		slog.Debug("user: successfully fetched user", "user ID", user.ID, "username", user.Name)
+		ctx := context.WithValue(r.Context(), userKey{}, user)
+		next.ServeHTTP(w, r.WithContext(ctx))
+	})
 }
 
 func ListUsers(w http.ResponseWriter, r *http.Request) {