package headscale import ( "bytes" "context" "crypto/rand" "encoding/hex" "errors" "fmt" "html/template" "net/http" "strings" "time" "github.com/coreos/go-oidc/v3/oidc" "github.com/gorilla/mux" "github.com/rs/zerolog/log" "golang.org/x/oauth2" "tailscale.com/types/key" ) const ( randomByteSize = 16 errEmptyOIDCCallbackParams = Error("empty OIDC callback params") errNoOIDCIDToken = Error("could not extract ID Token for OIDC callback") errOIDCAllowedDomains = Error("authenticated principal does not match any allowed domain") errOIDCAllowedUsers = Error("authenticated principal does not match any allowed user") errOIDCInvalidMachineState = Error("requested machine state key expired before authorisation completed") errOIDCNodeKeyMissing = Error("could not get node key from cache") ) type IDTokenClaims struct { Name string `json:"name,omitempty"` Groups []string `json:"groups,omitempty"` Email string `json:"email"` Username string `json:"preferred_username,omitempty"` } func (h *Headscale) initOIDC() error { var err error // grab oidc config if it hasn't been already if h.oauth2Config == nil { h.oidcProvider, err = oidc.NewProvider(context.Background(), h.cfg.OIDC.Issuer) if err != nil { log.Error(). Err(err). Caller(). Msgf("Could not retrieve OIDC Config: %s", err.Error()) return err } h.oauth2Config = &oauth2.Config{ ClientID: h.cfg.OIDC.ClientID, ClientSecret: h.cfg.OIDC.ClientSecret, Endpoint: h.oidcProvider.Endpoint(), RedirectURL: fmt.Sprintf( "%s/oidc/callback", strings.TrimSuffix(h.cfg.ServerURL, "/"), ), Scopes: h.cfg.OIDC.Scope, } } return nil } // RegisterOIDC redirects to the OIDC provider for authentication // Puts NodeKey in cache so the callback can retrieve it using the oidc state param // Listens in /oidc/register/:nKey. func (h *Headscale) RegisterOIDC( writer http.ResponseWriter, req *http.Request, ) { vars := mux.Vars(req) nodeKeyStr, ok := vars["nkey"] if !ok || nodeKeyStr == "" { log.Error(). Caller(). Msg("Missing node key in URL") http.Error(writer, "Missing node key in URL", http.StatusBadRequest) return } log.Trace(). Caller(). Str("node_key", nodeKeyStr). Msg("Received oidc register call") randomBlob := make([]byte, randomByteSize) if _, err := rand.Read(randomBlob); err != nil { log.Error(). Caller(). Msg("could not read 16 bytes from rand") http.Error(writer, "Internal server error", http.StatusInternalServerError) return } stateStr := hex.EncodeToString(randomBlob)[:32] // place the node key into the state cache, so it can be retrieved later h.registrationCache.Set(stateStr, nodeKeyStr, registerCacheExpiration) // Add any extra parameter provided in the configuration to the Authorize Endpoint request extras := make([]oauth2.AuthCodeOption, 0, len(h.cfg.OIDC.ExtraParams)) for k, v := range h.cfg.OIDC.ExtraParams { extras = append(extras, oauth2.SetAuthURLParam(k, v)) } authURL := h.oauth2Config.AuthCodeURL(stateStr, extras...) log.Debug().Msgf("Redirecting to %s for authentication", authURL) http.Redirect(writer, req, authURL, http.StatusFound) } type oidcCallbackTemplateConfig struct { User string Verb string } var oidcCallbackTemplate = template.Must( template.New("oidccallback").Parse(`

headscale

{{.Verb}} as {{.User}}, you can now close this window.

`), ) // OIDCCallback handles the callback from the OIDC endpoint // Retrieves the nkey from the state cache and adds the machine to the users email namespace // TODO: A confirmation page for new machines should be added to avoid phishing vulnerabilities // TODO: Add groups information from OIDC tokens into machine HostInfo // Listens in /oidc/callback. func (h *Headscale) OIDCCallback( writer http.ResponseWriter, req *http.Request, ) { code, state, err := validateOIDCCallbackParams(writer, req) if err != nil { return } rawIDToken, err := h.getIDTokenForOIDCCallback(req.Context(), writer, code, state) if err != nil { return } idToken, err := h.verifyIDTokenForOIDCCallback(req.Context(), writer, rawIDToken) if err != nil { return } // TODO: we can use userinfo at some point to grab additional information about the user (groups membership, etc) // userInfo, err := oidcProvider.UserInfo(context.Background(), oauth2.StaticTokenSource(oauth2Token)) // if err != nil { // c.String(http.StatusBadRequest, fmt.Sprintf("Failed to retrieve userinfo")) // return // } claims, err := extractIDTokenClaims(writer, idToken) if err != nil { return } if err := validateOIDCAllowedDomains(writer, h.cfg.OIDC.AllowedDomains, claims); err != nil { return } if err := validateOIDCAllowedUsers(writer, h.cfg.OIDC.AllowedUsers, claims); err != nil { return } nodeKey, machineExists, err := h.validateMachineForOIDCCallback(writer, state, claims) if err != nil || machineExists { return } namespaceName, err := getNamespaceName(writer, claims, h.cfg.OIDC.StripEmaildomain) if err != nil { return } // register the machine if it's new log.Debug().Msg("Registering new machine after successful callback") namespace, err := h.findOrCreateNewNamespaceForOIDCCallback(writer, namespaceName) if err != nil { return } if err := h.registerMachineForOIDCCallback(writer, namespace, nodeKey); err != nil { return } content, err := renderOIDCCallbackTemplate(writer, claims) if err != nil { return } writer.Header().Set("Content-Type", "text/html; charset=utf-8") writer.WriteHeader(http.StatusOK) if _, err := writer.Write(content.Bytes()); err != nil { log.Error(). Caller(). Err(err). Msg("Failed to write response") } } func validateOIDCCallbackParams( writer http.ResponseWriter, req *http.Request, ) (string, string, error) { code := req.URL.Query().Get("code") state := req.URL.Query().Get("state") if code == "" || state == "" { writer.Header().Set("Content-Type", "text/plain; charset=utf-8") writer.WriteHeader(http.StatusBadRequest) _, err := writer.Write([]byte("Wrong params")) if err != nil { log.Error(). Caller(). Err(err). Msg("Failed to write response") } return "", "", errEmptyOIDCCallbackParams } return code, state, nil } func (h *Headscale) getIDTokenForOIDCCallback( ctx context.Context, writer http.ResponseWriter, code, state string, ) (string, error) { oauth2Token, err := h.oauth2Config.Exchange(ctx, code) if err != nil { log.Error(). Err(err). Caller(). Msg("Could not exchange code for token") writer.Header().Set("Content-Type", "text/plain; charset=utf-8") writer.WriteHeader(http.StatusBadRequest) _, werr := writer.Write([]byte("Could not exchange code for token")) if werr != nil { log.Error(). Caller(). Err(werr). Msg("Failed to write response") } return "", err } log.Trace(). Caller(). Str("code", code). Str("state", state). Msg("Got oidc callback") rawIDToken, rawIDTokenOK := oauth2Token.Extra("id_token").(string) if !rawIDTokenOK { writer.Header().Set("Content-Type", "text/plain; charset=utf-8") writer.WriteHeader(http.StatusBadRequest) _, err := writer.Write([]byte("Could not extract ID Token")) if err != nil { log.Error(). Caller(). Err(err). Msg("Failed to write response") } return "", errNoOIDCIDToken } return rawIDToken, nil } func (h *Headscale) verifyIDTokenForOIDCCallback( ctx context.Context, writer http.ResponseWriter, rawIDToken string, ) (*oidc.IDToken, error) { verifier := h.oidcProvider.Verifier(&oidc.Config{ClientID: h.cfg.OIDC.ClientID}) idToken, err := verifier.Verify(ctx, rawIDToken) if err != nil { log.Error(). Err(err). Caller(). Msg("failed to verify id token") writer.Header().Set("Content-Type", "text/plain; charset=utf-8") writer.WriteHeader(http.StatusBadRequest) _, werr := writer.Write([]byte("Failed to verify id token")) if werr != nil { log.Error(). Caller(). Err(werr). Msg("Failed to write response") } return nil, err } return idToken, nil } func extractIDTokenClaims( writer http.ResponseWriter, idToken *oidc.IDToken, ) (*IDTokenClaims, error) { var claims IDTokenClaims if err := idToken.Claims(&claims); err != nil { log.Error(). Err(err). Caller(). Msg("Failed to decode id token claims") writer.Header().Set("Content-Type", "text/plain; charset=utf-8") writer.WriteHeader(http.StatusBadRequest) _, werr := writer.Write([]byte("Failed to decode id token claims")) if werr != nil { log.Error(). Caller(). Err(werr). Msg("Failed to write response") } return nil, err } return &claims, nil } // validateOIDCAllowedDomains checks that if AllowedDomains is provided, // that the authenticated principal ends with @. func validateOIDCAllowedDomains( writer http.ResponseWriter, allowedDomains []string, claims *IDTokenClaims, ) error { if len(allowedDomains) > 0 { if at := strings.LastIndex(claims.Email, "@"); at < 0 || !IsStringInSlice(allowedDomains, claims.Email[at+1:]) { log.Error().Msg("authenticated principal does not match any allowed domain") writer.Header().Set("Content-Type", "text/plain; charset=utf-8") writer.WriteHeader(http.StatusBadRequest) _, err := writer.Write([]byte("unauthorized principal (domain mismatch)")) if err != nil { log.Error(). Caller(). Err(err). Msg("Failed to write response") } return errOIDCAllowedDomains } } return nil } // validateOIDCAllowedUsers checks that if AllowedUsers is provided, // that the authenticated principal is part of that list. func validateOIDCAllowedUsers( writer http.ResponseWriter, allowedUsers []string, claims *IDTokenClaims, ) error { if len(allowedUsers) > 0 && !IsStringInSlice(allowedUsers, claims.Email) { log.Error().Msg("authenticated principal does not match any allowed user") writer.Header().Set("Content-Type", "text/plain; charset=utf-8") writer.WriteHeader(http.StatusBadRequest) _, err := writer.Write([]byte("unauthorized principal (user mismatch)")) if err != nil { log.Error(). Caller(). Err(err). Msg("Failed to write response") } return errOIDCAllowedUsers } return nil } // validateMachine retrieves machine information if it exist // The error is not important, because if it does not // exist, then this is a new machine and we will move // on to registration. func (h *Headscale) validateMachineForOIDCCallback( writer http.ResponseWriter, state string, claims *IDTokenClaims, ) (*key.NodePublic, bool, error) { // retrieve machinekey from state cache machineKeyIf, machineKeyFound := h.registrationCache.Get(state) if !machineKeyFound { log.Error(). Msg("requested machine state key expired before authorisation completed") writer.Header().Set("Content-Type", "text/plain; charset=utf-8") writer.WriteHeader(http.StatusBadRequest) _, err := writer.Write([]byte("state has expired")) if err != nil { log.Error(). Caller(). Err(err). Msg("Failed to write response") } return nil, false, errOIDCInvalidMachineState } var nodeKey key.NodePublic nodeKeyFromCache, nodeKeyOK := machineKeyIf.(string) err := nodeKey.UnmarshalText( []byte(NodePublicKeyEnsurePrefix(nodeKeyFromCache)), ) if err != nil { log.Error(). Msg("could not parse node public key") writer.Header().Set("Content-Type", "text/plain; charset=utf-8") writer.WriteHeader(http.StatusBadRequest) _, werr := writer.Write([]byte("could not parse public key")) if werr != nil { log.Error(). Caller(). Err(werr). Msg("Failed to write response") } return nil, false, err } if !nodeKeyOK { log.Error().Msg("could not get node key from cache") writer.Header().Set("Content-Type", "text/plain; charset=utf-8") writer.WriteHeader(http.StatusInternalServerError) _, err := writer.Write([]byte("could not get node key from cache")) if err != nil { log.Error(). Caller(). Err(err). Msg("Failed to write response") } return nil, false, errOIDCNodeKeyMissing } // retrieve machine information if it exist // The error is not important, because if it does not // exist, then this is a new machine and we will move // on to registration. machine, _ := h.GetMachineByNodeKey(nodeKey) if machine != nil { log.Trace(). Caller(). Str("machine", machine.Hostname). Msg("machine already registered, reauthenticating") err := h.RefreshMachine(machine, time.Time{}) if err != nil { log.Error(). Caller(). Err(err). Msg("Failed to refresh machine") http.Error( writer, "Failed to refresh machine", http.StatusInternalServerError, ) return nil, true, err } var content bytes.Buffer if err := oidcCallbackTemplate.Execute(&content, oidcCallbackTemplateConfig{ User: claims.Email, Verb: "Reauthenticated", }); err != nil { log.Error(). Str("func", "OIDCCallback"). Str("type", "reauthenticate"). Err(err). Msg("Could not render OIDC callback template") writer.Header().Set("Content-Type", "text/plain; charset=utf-8") writer.WriteHeader(http.StatusInternalServerError) _, werr := writer.Write([]byte("Could not render OIDC callback template")) if werr != nil { log.Error(). Caller(). Err(werr). Msg("Failed to write response") } return nil, true, err } writer.Header().Set("Content-Type", "text/html; charset=utf-8") writer.WriteHeader(http.StatusOK) _, err = writer.Write(content.Bytes()) if err != nil { log.Error(). Caller(). Err(err). Msg("Failed to write response") } return nil, true, nil } return &nodeKey, false, nil } func getNamespaceName( writer http.ResponseWriter, claims *IDTokenClaims, stripEmaildomain bool, ) (string, error) { namespaceName, err := NormalizeToFQDNRules( claims.Email, stripEmaildomain, ) if err != nil { log.Error().Err(err).Caller().Msgf("couldn't normalize email") writer.Header().Set("Content-Type", "text/plain; charset=utf-8") writer.WriteHeader(http.StatusInternalServerError) _, werr := writer.Write([]byte("couldn't normalize email")) if werr != nil { log.Error(). Caller(). Err(werr). Msg("Failed to write response") } return "", err } return namespaceName, nil } func (h *Headscale) findOrCreateNewNamespaceForOIDCCallback( writer http.ResponseWriter, namespaceName string, ) (*Namespace, error) { namespace, err := h.GetNamespace(namespaceName) if errors.Is(err, ErrNamespaceNotFound) { namespace, err = h.CreateNamespace(namespaceName) if err != nil { log.Error(). Err(err). Caller(). Msgf("could not create new namespace '%s'", namespaceName) writer.Header().Set("Content-Type", "text/plain; charset=utf-8") writer.WriteHeader(http.StatusInternalServerError) _, werr := writer.Write([]byte("could not create namespace")) if werr != nil { log.Error(). Caller(). Err(werr). Msg("Failed to write response") } return nil, err } } else if err != nil { log.Error(). Caller(). Err(err). Str("namespace", namespaceName). Msg("could not find or create namespace") writer.Header().Set("Content-Type", "text/plain; charset=utf-8") writer.WriteHeader(http.StatusInternalServerError) _, werr := writer.Write([]byte("could not find or create namespace")) if werr != nil { log.Error(). Caller(). Err(werr). Msg("Failed to write response") } return nil, err } return namespace, nil } func (h *Headscale) registerMachineForOIDCCallback( writer http.ResponseWriter, namespace *Namespace, nodeKey *key.NodePublic, ) error { nodeKeyStr := NodePublicKeyStripPrefix(*nodeKey) if _, err := h.RegisterMachineFromAuthCallback( nodeKeyStr, namespace.Name, RegisterMethodOIDC, ); err != nil { log.Error(). Caller(). Err(err). Msg("could not register machine") writer.Header().Set("Content-Type", "text/plain; charset=utf-8") writer.WriteHeader(http.StatusInternalServerError) _, werr := writer.Write([]byte("could not register machine")) if werr != nil { log.Error(). Caller(). Err(werr). Msg("Failed to write response") } return err } return nil } func renderOIDCCallbackTemplate( writer http.ResponseWriter, claims *IDTokenClaims, ) (*bytes.Buffer, error) { var content bytes.Buffer if err := oidcCallbackTemplate.Execute(&content, oidcCallbackTemplateConfig{ User: claims.Email, Verb: "Authenticated", }); err != nil { log.Error(). Str("func", "OIDCCallback"). Str("type", "authenticate"). Err(err). Msg("Could not render OIDC callback template") writer.Header().Set("Content-Type", "text/plain; charset=utf-8") writer.WriteHeader(http.StatusInternalServerError) _, werr := writer.Write([]byte("Could not render OIDC callback template")) if werr != nil { log.Error(). Caller(). Err(werr). Msg("Failed to write response") } return nil, err } return &content, nil }