auth.go

// Copyright 2020 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Package middleware defines shared middleware for handlers.
package middleware

import (
	"context"
	"fmt"
	"net/http"
	"time"

	"github.com/google/exposure-notifications-verification-server/pkg/cache"
	"github.com/google/exposure-notifications-verification-server/pkg/controller"
	"github.com/google/exposure-notifications-verification-server/pkg/database"
	"github.com/google/exposure-notifications-verification-server/pkg/render"

	"github.com/google/exposure-notifications-server/pkg/logging"

	"firebase.google.com/go/auth"
	"github.com/gorilla/mux"
)

// RequireAuth requires a user to be logged in. It also ensures that currentUser
// is set in the template map. It fetches a user from the session and stores the
// full record in the request context.
func RequireAuth(ctx context.Context, cacher cache.Cacher, fbClient *auth.Client, db *database.Database, h *render.Renderer, ttl time.Duration) mux.MiddlewareFunc {
	logger := logging.FromContext(ctx).Named("middleware.RequireAuth")

	cacheTTL := 5 * time.Minute

	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			ctx := r.Context()

			session := controller.SessionFromContext(ctx)
			if session == nil {
				logger.Errorw("session does not exist")
				controller.MissingSession(w, r, h)
				return
			}

			flash := controller.Flash(session)

			firebaseCookie := controller.FirebaseCookieFromSession(session)
			if firebaseCookie == "" {
				logger.Debugw("firebase cookie not in session")
				flash.Error("An error occurred trying to verify your credentials.")
				controller.Unauthorized(w, r, h)
				return
			}

			email, err := EmailFromFirebaseCookie(ctx, fbClient, firebaseCookie)
			if err != nil {
				controller.ClearSessionFirebaseCookie(session)

				logger.Debugw("failed to extract email from firebase cookie", "error", err)
				flash.Error("Your credentials are invalid. Clear your cookies and try again.")
				controller.Unauthorized(w, r, h)
				return
			}

			// Load the user by using the cache to alleviate pressure on the database
			// layer.
			var user database.User
			cacheKey := fmt.Sprintf("users:by_email:%s", email)
			if err := cacher.Fetch(ctx, cacheKey, &user, cacheTTL, func() (interface{}, error) {
				return db.FindUserByEmail(email)
			}); err != nil {
				controller.ClearSessionFirebaseCookie(session)

				if database.IsNotFound(err) {
					logger.Debugw("user does not exist")
					controller.Unauthorized(w, r, h)
					return
				}

				logger.Errorw("failed to lookup user", "error", err)
				controller.InternalError(w, r, h, err)
				return
			}

			// Check if the session is still valid.
			if time.Now().After(user.LastRevokeCheck.Add(ttl)) {
				if _, err := fbClient.VerifySessionCookieAndCheckRevoked(ctx, firebaseCookie); err != nil {
					logger.Debugw("failed to verify firebase cookie revocation", "error", err)
					controller.ClearSessionFirebaseCookie(session)
					controller.Unauthorized(w, r, h)
					return
				}

				// Update the revoke check time.
				if err := db.TouchUserRevokeCheck(&user); err != nil {
					logger.Errorw("failed to update revocation check time", "error", err)
					controller.InternalError(w, r, h, err)
					return
				}

				// Update the user in the cache so it has the new revoke check time.
				if err := cacher.Write(ctx, cacheKey, &user, 30*time.Second); err != nil {
					logger.Errorw("failed to cached user revocation check time", "error", err)
					controller.InternalError(w, r, h, err)
					return
				}
			}

			// Save the user on the context.
			ctx = controller.WithUser(ctx, &user)
			*r = *r.WithContext(ctx)

			next.ServeHTTP(w, r)
		})
	}
}

// EmailFromFirebaseCookie extracts the user's email address from the provided
// firebase cookie, if it exists.
func EmailFromFirebaseCookie(ctx context.Context, fbClient *auth.Client, cookie string) (string, error) {
	token, err := fbClient.VerifySessionCookie(ctx, cookie)
	if err != nil {
		return "", fmt.Errorf("failed to verify firebase cookie: %w", err)
	}

	if token.Claims == nil || token.Claims["email"] == nil {
		return "", fmt.Errorf("missing token claims for email")
	}

	email, ok := token.Claims["email"].(string)
	if !ok {
		return "", fmt.Errorf("token claims for email are not a string")
	}
	return email, nil
}

// RequireAdmin requires the current user is a global administrator. It must
// come after RequireAuth so that a user is set on the context.
func RequireAdmin(ctx context.Context, h *render.Renderer) mux.MiddlewareFunc {
	logger := logging.FromContext(ctx).Named("middleware.RequireAdminHandler")

	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			ctx := r.Context()

			user := controller.UserFromContext(ctx)
			if user == nil {
				controller.MissingUser(w, r, h)
				return
			}

			if !user.Admin {
				logger.Debugw("user is not an admin")
				controller.Unauthorized(w, r, h)
				return
			}

			next.ServeHTTP(w, r)
		})
	}
}