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lib.go
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lib.go
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// Package google_oauth_handler transparently handles OAuth authentication with
// Google.
//
// Create an Authenticator and then insert it as middleware in front of any
// resources you want to protect behind Google login, via authenticator.Handle.
// Handle will call the next middleware with (w, r, *Token), which you can use
// to make requests to the Google API.
//
// The Authenticator handles the OAuth workflow for you, redirecting users to
// Google, handling the callback and setting an encrypted cookie in the user's
// browser.
package google_oauth_handler
import (
"context"
"encoding/json"
"errors"
"fmt"
"net/http"
"net/mail"
"net/url"
"sync"
"time"
log "github.com/inconshreveable/log15"
"github.com/kevinburke/handlers"
"github.com/kevinburke/rest"
"golang.org/x/oauth2"
"golang.org/x/oauth2/google"
)
const Version = "0.5"
// DefaultExpiry is the duration of a valid cookie.
var DefaultExpiry = 14 * 24 * time.Hour
// AuthTimeout is the amount of time to allow users to complete an
// authentication attempt.
var AuthTimeout = 1 * time.Hour
// Timeout is the amount of time to wait for a response from Google when asking
// for information.
var Timeout = 30 * time.Second
const cookieName = "google-oauth-token"
// Config allows users to configure an Authenticator.
type Config struct {
// The logger to use for logging errors in the authentication workflow.
Logger log.Logger
// BaseURL is the server's base URL (scheme+host), used to set cookies.
BaseURL string
// SecretKey is used to encrypt and decrypt the OAuth nonce and cookies.
SecretKey *[32]byte
// The Google ClientID and Secret. To figure out how to get these, visit
// https://github.com/saintpete/logrole/blob/master/docs/google.md
ClientID string
Secret string
// List of scopes (a.k.a permissions) to ask for.
// For a list of valid scopes see https://developers.google.com/identity/protocols/googlescopes.
Scopes []string
// Set to "false" to set Secure: false on cookies.
AllowUnencryptedTraffic bool
// If non-empty, limit access to users with email addresses in these domains.
AllowedDomains []string
// ServeLogin will be called when the user needs to authenticate with
// Google, for example if you want to display a custom login page with
// a "Log in with Google" button.
//
// If ServeLogin is nil, all users that need to authenticate will be
// immediately redirected to Google.
ServeLogin http.Handler
// Which URL Google should hit when they redirect users back to your site
// after logging in. Defaults to "/auth/callback".
CallbackPath string
}
// Auth is returned in the callback to Handle().
type Auth struct {
// The Google email address for this user.
Email *mail.Address
// A Client that's configured to use the Google credentials
Client *http.Client
Token *oauth2.Token
}
// An Authenticator transparently handles authentication with Google. Create an
// Authenticator by calling NewAuthenticator(Config{}).
type Authenticator struct {
logger log.Logger
conf *oauth2.Config
allowUnencryptedTraffic bool
callback string
allowedDomains []string
secretKey *[32]byte
// Login gets called when the user must authenticate. The default Login
// behavior is to redirect to the Google authentication page.
login http.Handler
loginMu sync.Mutex
}
// SetLogin sets the login handler to h. A convenience handler since this may be
// configured later than the other parts of the google oauth handler's config.
func (a *Authenticator) SetLogin(h http.Handler) {
a.loginMu.Lock()
a.login = h
a.loginMu.Unlock()
}
// NewAuthenticator creates a new Authenticator that can
// authenticate requests via Google login.
//
// To get a clientID and clientSecret, see
// https://github.com/saintpete/logrole/blob/master/docs/google.md.
func NewAuthenticator(c Config) *Authenticator {
if c.CallbackPath == "" {
c.CallbackPath = "/auth/callback"
}
conf := &oauth2.Config{
ClientID: c.ClientID,
ClientSecret: c.Secret,
RedirectURL: c.BaseURL + c.CallbackPath,
// https://developers.google.com/identity/protocols/googlescopes#google_sign-in
Scopes: c.Scopes,
Endpoint: google.Endpoint,
}
if c.Logger == nil {
c.Logger = handlers.Logger
}
a := &Authenticator{
logger: c.Logger,
conf: conf,
allowUnencryptedTraffic: c.AllowUnencryptedTraffic,
allowedDomains: c.AllowedDomains,
secretKey: c.SecretKey,
callback: c.CallbackPath,
}
// no need to lock since no one else can call till it's returned
if c.ServeLogin == nil {
a.login = http.HandlerFunc(a.defaultLogin)
} else {
a.login = c.ServeLogin
}
return a
}
// Logout wipes the Google authentication cookie from w.
func (a *Authenticator) Logout(w http.ResponseWriter) {
http.SetCookie(w, &http.Cookie{
Name: cookieName,
Path: "/",
MaxAge: -1,
Expires: time.Unix(1, 0),
})
}
// URL returns a link to the Google auth URL for this Authenticator. If
// the http.Request contains a query parameter named "g", the user will be
// redirected to that page upon returning from Google.
func (a *Authenticator) URL(r *http.Request) string {
var uri string
if g := r.URL.Query().Get("g"); g != "" {
// prevent open redirect by only using the Path part
u, err := url.Parse(g)
if err == nil {
uri = u.Path
} else {
uri = r.URL.RequestURI()
}
} else {
uri = r.URL.RequestURI()
}
st := state{
CurrentURL: uri,
Time: time.Now().UTC(),
}
bits, err := json.Marshal(st)
if err != nil {
panic(err)
}
encoded := opaqueByte(bits, a.secretKey)
return a.conf.AuthCodeURL(encoded)
}
// defaultLogin redirects the request to the Google authentication URL.
func (a *Authenticator) defaultLogin(w http.ResponseWriter, r *http.Request) {
u := a.URL(r)
http.Redirect(w, r, u, http.StatusFound)
}
func (a *Authenticator) validState(encrypted string) (string, bool) {
b, err := unopaqueByte(encrypted, a.secretKey)
if err != nil {
return "", false
}
st := new(state)
if err := json.Unmarshal(b, st); err != nil {
return "", false
}
if time.Since(st.Time) > AuthTimeout {
return "", false
}
return st.CurrentURL, true
}
// Handle returns an http.Handler that only calls f if the request carries
// a valid authentication cookie. If not, a.Login is called, to trigger an
// authentication workflow with Google. If the user approves access for the
// provided scopes, we set an encrypted cookie on the request and call f(w, r,
// token). The token can then be used to make requests to Google's APIs.
//
// Handle must handle requests to the CallbackPath (which defaults to
// /auth/callback) in order to set a valid cookie.
func (a *Authenticator) Handle(f func(http.ResponseWriter, *http.Request, *Auth)) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
if r.URL.Path == a.callback {
a.handleGoogleCallback(w, r)
return
}
a.loginMu.Lock()
login := a.login
a.loginMu.Unlock()
// Check if the request has a valid cookie, if not redirect to login.
cookie, err := r.Cookie(cookieName)
if err != nil {
login.ServeHTTP(w, r)
return
}
val, err := unopaqueByte(cookie.Value, a.secretKey)
if err != nil {
// Bad cookie. TODO need a 400 bad request here
login.ServeHTTP(w, r)
return
}
t := new(token)
if err := json.Unmarshal(val, t); err != nil {
// TODO clear it
login.ServeHTTP(w, r)
return
}
now := time.Now().UTC()
if t.Expiry.Before(now) {
// TODO logout
login.ServeHTTP(w, r)
return
}
// It's possible the AccessToken has expired by the time the user makes
// a request. We don't want to log them out, so try to refresh the token
// now if necessary.
src := a.conf.TokenSource(wctx(r), t.Token)
newToken, err := src.Token()
if err != nil {
// some sort of error getting a token, ask user to log in again.
login.ServeHTTP(w, r)
return
}
if t.Token.AccessToken != newToken.AccessToken {
// we got a new token
t.Token = newToken
cookie := a.newCookie(t)
http.SetCookie(w, cookie)
}
// todo - not super happy with this.
f(w, r, &Auth{
t.Email,
a.conf.Client(wctx(r), t.Token),
t.Token,
})
})
}
func (a *Authenticator) handleGoogleCallback(w http.ResponseWriter, r *http.Request) error {
query := r.URL.Query()
st := query.Get("state")
currentURL, ok := a.validState(st)
if !ok {
http.Redirect(w, r, "/", 302)
return errors.New("invalid state")
}
code := query.Get("code")
if code == "" {
a.logger.Warn("Callback request has valid state, no code")
http.Redirect(w, r, "/", 302)
return errors.New("invalid state")
}
ctx, cancel := context.WithTimeout(wctx(r), Timeout)
defer cancel()
tok, err := a.conf.Exchange(ctx, code)
if err != nil {
// TODO this can return 400+JSON if you try to redeem a code twice:
// Response: {
// "error" : "invalid_grant",
// "error_description" : "Invalid code."
// }
rest.ServerError(w, r, err)
return err
}
client := a.conf.Client(ctx, tok)
u, err := getGoogleUserData(ctx, client)
if err != nil {
rest.ServerError(w, r, err)
return err
}
// TODO verify allowed domains.
t := newToken(u.Address(), tok)
cookie := a.newCookie(t)
http.SetCookie(w, cookie)
http.Redirect(w, r, currentURL, 302)
return errors.New("redirected, make another request")
}
func (a *Authenticator) newCookie(t *token) *http.Cookie {
b, err := json.Marshal(t)
if err != nil {
panic(err)
}
text := opaqueByte(b, a.secretKey)
return &http.Cookie{
Name: cookieName,
Value: text,
Path: "/",
Secure: a.allowUnencryptedTraffic == false,
Expires: t.Expiry,
HttpOnly: true,
}
}
type token struct {
Email *mail.Address
Token *oauth2.Token
Expiry time.Time
}
type state struct {
CurrentURL string
Time time.Time
}
func newToken(id *mail.Address, tok *oauth2.Token) *token {
return &token{
Email: id,
Token: tok,
Expiry: time.Now().UTC().Add(DefaultExpiry),
}
}
// Base URL to get user data from.
var userDataBase = "https://www.googleapis.com"
// Path that allows you to get user data.
var userDataPath = "/oauth2/v3/userinfo"
// The data about users that we get back from Google.
type googleUser struct {
Sub string `json:"sub"`
Name string `json:"name"`
GivenName string `json:"given_name"`
FamilyName string `json:"family_name"`
Profile string `json:"profile"`
Picture string `json:"picture"`
Email string `json:"email"`
EmailVerified bool `json:"email_verified"`
Gender string `json:"gender"`
Locale string `json:"locale"`
HD string `json:"hd"`
}
func (g *googleUser) Address() *mail.Address {
return &mail.Address{
Name: g.Name,
Address: g.Email,
}
}
func getGoogleUserData(ctx context.Context, client *http.Client) (*googleUser, error) {
if client == nil {
client = http.DefaultClient
}
rc := rest.NewClient("", "", userDataBase)
rc.Client = client
req, err := rc.NewRequest("GET", userDataPath, nil)
if err != nil {
return nil, err
}
req = req.WithContext(ctx)
u := new(googleUser)
err = rc.Do(req, u)
if err != nil {
return nil, err
}
if u.Email == "" {
return nil, fmt.Errorf("No email address for user: %s", u.Name)
}
if _, err := mail.ParseAddress(u.Email); err != nil {
return nil, err
}
if u.EmailVerified == false {
return nil, fmt.Errorf("User %s does not have a verified email address", u.Name)
}
return u, err
}