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/gin-gonic/gin"
"github.com/rs/zerolog/log"
"golang.org/x/oauth2"
"tailscale.com/types/key"
)
const (
randomByteSize = 16
)
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 machine key in cache so the callback can retrieve it using the oidc state param
// Listens in /oidc/register/:mKey.
func (h *Headscale) RegisterOIDC(ctx *gin.Context) {
machineKeyStr := ctx.Param("mkey")
if machineKeyStr == "" {
ctx.String(http.StatusBadRequest, "Wrong params")
return
}
log.Trace().
Caller().
Str("machine_key", machineKeyStr).
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")
ctx.String(http.StatusInternalServerError, "could not read 16 bytes from rand")
return
}
stateStr := hex.EncodeToString(randomBlob)[:32]
// place the machine key into the state cache, so it can be retrieved later
h.registrationCache.Set(stateStr, machineKeyStr, 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)
ctx.Redirect(http.StatusFound, authURL)
}
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 mkey 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(ctx *gin.Context) {
code := ctx.Query("code")
state := ctx.Query("state")
if code == "" || state == "" {
ctx.String(http.StatusBadRequest, "Wrong params")
return
}
oauth2Token, err := h.oauth2Config.Exchange(context.Background(), code)
if err != nil {
log.Error().
Err(err).
Caller().
Msg("Could not exchange code for token")
ctx.String(http.StatusBadRequest, "Could not exchange code for token")
return
}
log.Trace().
Caller().
Str("code", code).
Str("state", state).
Msg("Got oidc callback")
rawIDToken, rawIDTokenOK := oauth2Token.Extra("id_token").(string)
if !rawIDTokenOK {
ctx.String(http.StatusBadRequest, "Could not extract ID Token")
return
}
verifier := h.oidcProvider.Verifier(&oidc.Config{ClientID: h.cfg.OIDC.ClientID})
idToken, err := verifier.Verify(context.Background(), rawIDToken)
if err != nil {
log.Error().
Err(err).
Caller().
Msg("failed to verify id token")
ctx.String(http.StatusBadRequest, "Failed to verify id token")
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
// }
// Extract custom claims
var claims IDTokenClaims
if err = idToken.Claims(&claims); err != nil {
log.Error().
Err(err).
Caller().
Msg("Failed to decode id token claims")
ctx.String(
http.StatusBadRequest,
"Failed to decode id token claims",
)
return
}
// If AllowedDomains is provided, check that the authenticated principal ends with @.
if len(h.cfg.OIDC.AllowedDomains) > 0 {
if at := strings.LastIndex(claims.Email, "@"); at < 0 ||
!IsStringInSlice(h.cfg.OIDC.AllowedDomains, claims.Email[at+1:]) {
log.Error().Msg("authenticated principal does not match any allowed domain")
ctx.String(
http.StatusBadRequest,
"unauthorized principal (domain mismatch)",
)
return
}
}
// If AllowedUsers is provided, check that the authenticated princial is part of that list.
if len(h.cfg.OIDC.AllowedUsers) > 0 &&
!IsStringInSlice(h.cfg.OIDC.AllowedUsers, claims.Email) {
log.Error().Msg("authenticated principal does not match any allowed user")
ctx.String(http.StatusBadRequest, "unauthorized principal (user mismatch)")
return
}
// retrieve machinekey from state cache
machineKeyIf, machineKeyFound := h.registrationCache.Get(state)
if !machineKeyFound {
log.Error().
Msg("requested machine state key expired before authorisation completed")
ctx.String(http.StatusBadRequest, "state has expired")
return
}
machineKeyFromCache, machineKeyOK := machineKeyIf.(string)
var machineKey key.MachinePublic
err = machineKey.UnmarshalText(
[]byte(MachinePublicKeyEnsurePrefix(machineKeyFromCache)),
)
if err != nil {
log.Error().
Msg("could not parse machine public key")
ctx.String(http.StatusBadRequest, "could not parse public key")
return
}
if !machineKeyOK {
log.Error().Msg("could not get machine key from cache")
ctx.String(
http.StatusInternalServerError,
"could not get machine key from cache",
)
return
}
// 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.GetMachineByMachineKey(machineKey)
if machine != nil {
log.Trace().
Caller().
Str("machine", machine.Hostname).
Msg("machine already registered, reauthenticating")
h.RefreshMachine(machine, time.Time{})
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")
ctx.Data(
http.StatusInternalServerError,
"text/html; charset=utf-8",
[]byte("Could not render OIDC callback template"),
)
}
ctx.Data(http.StatusOK, "text/html; charset=utf-8", content.Bytes())
return
}
namespaceName, err := NormalizeToFQDNRules(
claims.Email,
h.cfg.OIDC.StripEmaildomain,
)
if err != nil {
log.Error().Err(err).Caller().Msgf("couldn't normalize email")
ctx.String(
http.StatusInternalServerError,
"couldn't normalize email",
)
return
}
// register the machine if it's new
log.Debug().Msg("Registering new machine after successful callback")
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)
ctx.String(
http.StatusInternalServerError,
"could not create new namespace",
)
return
}
} else if err != nil {
log.Error().
Caller().
Err(err).
Str("namespace", namespaceName).
Msg("could not find or create namespace")
ctx.String(
http.StatusInternalServerError,
"could not find or create namespace",
)
return
}
machineKeyStr := MachinePublicKeyStripPrefix(machineKey)
_, err = h.RegisterMachineFromAuthCallback(
machineKeyStr,
namespace.Name,
RegisterMethodOIDC,
)
if err != nil {
log.Error().
Caller().
Err(err).
Msg("could not register machine")
ctx.String(
http.StatusInternalServerError,
"could not register machine",
)
return
}
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")
ctx.Data(
http.StatusInternalServerError,
"text/html; charset=utf-8",
[]byte("Could not render OIDC callback template"),
)
}
ctx.Data(http.StatusOK, "text/html; charset=utf-8", content.Bytes())
}