package providers import ( "bytes" "encoding/base64" "encoding/json" "errors" "fmt" "io" "io/ioutil" "log" "net/http" "net/url" "strings" "time" "golang.org/x/oauth2" "golang.org/x/oauth2/google" "google.golang.org/api/admin/directory/v1" ) type GoogleProvider struct { *ProviderData RedeemRefreshURL *url.URL // GroupValidator is a function that determines if the passed email is in // the configured Google group. GroupValidator func(string) bool } func NewGoogleProvider(p *ProviderData) *GoogleProvider { p.ProviderName = "Google" if p.LoginURL.String() == "" { p.LoginURL = &url.URL{Scheme: "https", Host: "accounts.google.com", Path: "/o/oauth2/auth", // to get a refresh token. see https://developers.google.com/identity/protocols/OAuth2WebServer#offline RawQuery: "access_type=offline", } } if p.RedeemURL.String() == "" { p.RedeemURL = &url.URL{Scheme: "https", Host: "www.googleapis.com", Path: "/oauth2/v3/token"} } if p.ValidateURL.String() == "" { p.ValidateURL = &url.URL{Scheme: "https", Host: "www.googleapis.com", Path: "/oauth2/v1/tokeninfo"} } if p.Scope == "" { p.Scope = "profile email" } return &GoogleProvider{ ProviderData: p, // Set a default GroupValidator to just always return valid (true), it will // be overwritten if we configured a Google group restriction. GroupValidator: func(email string) bool { return true }, } } func emailFromIdToken(idToken string) (string, error) { // id_token is a base64 encode ID token payload // https://developers.google.com/accounts/docs/OAuth2Login#obtainuserinfo jwt := strings.Split(idToken, ".") b, err := jwtDecodeSegment(jwt[1]) if err != nil { return "", err } var email struct { Email string `json:"email"` EmailVerified bool `json:"email_verified"` } err = json.Unmarshal(b, &email) if err != nil { return "", err } if email.Email == "" { return "", errors.New("missing email") } if !email.EmailVerified { return "", fmt.Errorf("email %s not listed as verified", email.Email) } return email.Email, nil } func jwtDecodeSegment(seg string) ([]byte, error) { if l := len(seg) % 4; l > 0 { seg += strings.Repeat("=", 4-l) } return base64.URLEncoding.DecodeString(seg) } func (p *GoogleProvider) Redeem(redirectURL, code string) (s *SessionState, err error) { if code == "" { err = errors.New("missing code") return } params := url.Values{} params.Add("redirect_uri", redirectURL) params.Add("client_id", p.ClientID) params.Add("client_secret", p.ClientSecret) params.Add("code", code) params.Add("grant_type", "authorization_code") var req *http.Request req, err = http.NewRequest("POST", p.RedeemURL.String(), bytes.NewBufferString(params.Encode())) if err != nil { return } req.Header.Set("Content-Type", "application/x-www-form-urlencoded") resp, err := http.DefaultClient.Do(req) if err != nil { return } var body []byte body, err = ioutil.ReadAll(resp.Body) resp.Body.Close() if err != nil { return } if resp.StatusCode != 200 { err = fmt.Errorf("got %d from %q %s", resp.StatusCode, p.RedeemURL.String(), body) return } var jsonResponse struct { AccessToken string `json:"access_token"` RefreshToken string `json:"refresh_token"` ExpiresIn int64 `json:"expires_in"` IdToken string `json:"id_token"` } err = json.Unmarshal(body, &jsonResponse) if err != nil { return } var email string email, err = emailFromIdToken(jsonResponse.IdToken) if err != nil { return } s = &SessionState{ AccessToken: jsonResponse.AccessToken, ExpiresOn: time.Now().Add(time.Duration(jsonResponse.ExpiresIn) * time.Second).Truncate(time.Second), RefreshToken: jsonResponse.RefreshToken, Email: email, } return } // SetGroupRestriction configures the GoogleProvider to restrict access to the // specified group(s). AdminEmail has to be an administrative email on the domain that is // checked. CredentialsFile is the path to a json file containing a Google service // account credentials. func (p *GoogleProvider) SetGroupRestriction(groups []string, adminEmail string, credentialsReader io.Reader) { adminService := getAdminService(adminEmail, credentialsReader) p.GroupValidator = func(email string) bool { return userInGroup(adminService, groups, email) } } func getAdminService(adminEmail string, credentialsReader io.Reader) *admin.Service { data, err := ioutil.ReadAll(credentialsReader) if err != nil { log.Fatal("can't read Google credentials file:", err) } conf, err := google.JWTConfigFromJSON(data, admin.AdminDirectoryUserReadonlyScope, admin.AdminDirectoryGroupReadonlyScope) if err != nil { log.Fatal("can't load Google credentials file:", err) } conf.Subject = adminEmail client := conf.Client(oauth2.NoContext) adminService, err := admin.New(client) if err != nil { log.Fatal(err) } return adminService } func userInGroup(service *admin.Service, groups []string, email string) bool { user, err := fetchUser(service, email) if err != nil { log.Printf("error fetching user: %v", err) return false } id := user.Id custID := user.CustomerId for _, group := range groups { members, err := fetchGroupMembers(service, group) if err != nil { log.Printf("error fetching group members: %v", err) return false } for _, member := range members { switch member.Type { case "CUSTOMER": if member.Id == custID { return true } case "USER": if member.Id == id { return true } } } } return false } func fetchUser(service *admin.Service, email string) (*admin.User, error) { user, err := service.Users.Get(email).Do() return user, err } func fetchGroupMembers(service *admin.Service, group string) ([]*admin.Member, error) { members := []*admin.Member{} pageToken := "" for { req := service.Members.List(group) if pageToken != "" { req.PageToken(pageToken) } r, err := req.Do() if err != nil { return nil, err } for _, member := range r.Members { members = append(members, member) } if r.NextPageToken == "" { break } pageToken = r.NextPageToken } return members, nil } // ValidateGroup validates that the provided email exists in the configured Google // group(s). func (p *GoogleProvider) ValidateGroup(email string) bool { return p.GroupValidator(email) } func (p *GoogleProvider) RefreshSessionIfNeeded(s *SessionState) (bool, error) { if s == nil || s.ExpiresOn.After(time.Now()) || s.RefreshToken == "" { return false, nil } newToken, duration, err := p.redeemRefreshToken(s.RefreshToken) if err != nil { return false, err } // re-check that the user is in the proper google group(s) if !p.ValidateGroup(s.Email) { return false, fmt.Errorf("%s is no longer in the group(s)", s.Email) } origExpiration := s.ExpiresOn s.AccessToken = newToken s.ExpiresOn = time.Now().Add(duration).Truncate(time.Second) log.Printf("refreshed access token %s (expired on %s)", s, origExpiration) return true, nil } func (p *GoogleProvider) redeemRefreshToken(refreshToken string) (token string, expires time.Duration, err error) { // https://developers.google.com/identity/protocols/OAuth2WebServer#refresh params := url.Values{} params.Add("client_id", p.ClientID) params.Add("client_secret", p.ClientSecret) params.Add("refresh_token", refreshToken) params.Add("grant_type", "refresh_token") var req *http.Request req, err = http.NewRequest("POST", p.RedeemURL.String(), bytes.NewBufferString(params.Encode())) if err != nil { return } req.Header.Set("Content-Type", "application/x-www-form-urlencoded") resp, err := http.DefaultClient.Do(req) if err != nil { return } var body []byte body, err = ioutil.ReadAll(resp.Body) resp.Body.Close() if err != nil { return } if resp.StatusCode != 200 { err = fmt.Errorf("got %d from %q %s", resp.StatusCode, p.RedeemURL.String(), body) return } var data struct { AccessToken string `json:"access_token"` ExpiresIn int64 `json:"expires_in"` } err = json.Unmarshal(body, &data) if err != nil { return } token = data.AccessToken expires = time.Duration(data.ExpiresIn) * time.Second return }