// The tsidp command is an OpenID Connect Identity Provider server.
package main
import (
"context"
crand "crypto/rand"
"crypto/rsa"
"crypto/x509"
"encoding/base64"
"encoding/binary"
"encoding/json"
"encoding/pem"
"flag"
"fmt"
"io"
"log"
"net/http"
"net/netip"
"os"
"strings"
"sync"
"github.com/golang-jwt/jwt"
"gopkg.in/square/go-jose.v2"
"tailscale.com/client/tailscale"
"tailscale.com/tailcfg"
"tailscale.com/tsnet"
"tailscale.com/tsweb"
"tailscale.com/types/key"
"tailscale.com/types/logger"
"tailscale.com/types/views"
"tailscale.com/util/must"
)
var (
flagVerbose = flag.Bool("verbose", false, "be verbose")
)
func main() {
flag.Parse()
ctx := context.Background()
ts := &tsnet.Server{
Hostname: "idp",
}
if !*flagVerbose {
ts.Logf = logger.Discard
}
st, err := ts.Up(ctx)
if err != nil {
log.Fatal(err)
}
lc, err := ts.LocalClient()
if err != nil {
log.Fatalf("getting local client: %v", err)
}
srv := &idpServer{
lc: lc,
serverURL: "https://" + strings.TrimSuffix(st.Self.DNSName, "."),
}
log.Printf("Running tsidp at %s ...", srv.serverURL)
ln, err := ts.ListenTLS("tcp", ":443")
if err != nil {
log.Fatal(err)
}
log.Fatal(http.Serve(ln, srv))
}
type idpServer struct {
lc *tailscale.LocalClient
serverURL string // "https://foo.bar.ts.net"
oidcSignerInitOnce sync.Once
oidcSignerLazy jose.Signer
oidcSignerError error
}
func (s *idpServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
log.Printf("%v %v", r.Method, r.URL)
if r.URL.Path == oidcJWKSPath {
if err := s.serveJWKS(w, r); err != nil {
log.Printf("Error serving JWKS: %v", err)
}
return
}
if r.URL.Path == oidcConfigPath {
if err := s.serveOpenIDConfig(w, r); err != nil {
log.Printf("Error serving OpenID config: %v", err)
}
return
}
if r.URL.Path == "/" {
io.WriteString(w, "Tailscale OIDC IdP
")
return
}
if r.URL.Path == "/authorize" {
redir := r.URL.Query().Get("redirect_uri")
http.Redirect(w, r, redir, http.StatusFound)
return
}
http.Error(w, "tsidp: not found", http.StatusNotFound)
}
const (
oidcJWKSPath = "/.well-known/jwks.json"
oidcConfigPath = "/.well-known/openid-configuration"
)
func (s *idpServer) oidcSigner() (jose.Signer, error) {
s.oidcSignerInitOnce.Do(s.oidcSignerInit)
return s.oidcSignerLazy, s.oidcSignerError
}
func (s *idpServer) oidcSignerInit() {
id, k := s.oidcPrivateKey()
s.oidcSignerLazy, s.oidcSignerError = jose.NewSigner(jose.SigningKey{
Algorithm: jose.RS256,
Key: k,
}, &jose.SignerOptions{EmbedJWK: false, ExtraHeaders: map[jose.HeaderKey]interface{}{
jose.HeaderType: "JWT",
"kid": fmt.Sprint(id),
}})
}
func (s *idpServer) oidcPrivateKey() (id uint64, k *rsa.PrivateKey) {
id, k = mustGenRSAKey(2048)
return
}
func (s *idpServer) serveJWKS(w http.ResponseWriter, r *http.Request) error {
if r.URL.Path != oidcJWKSPath {
return tsweb.Error(404, "", nil)
}
w.Header().Set("Content-Type", "application/json")
id, k := s.oidcPrivateKey()
// TODO(maisem): maybe only marshal this once and reuse?
// TODO(maisem): implement key rotation.
if err := json.NewEncoder(w).Encode(jose.JSONWebKeySet{
Keys: []jose.JSONWebKey{
{
Key: k.Public(),
Algorithm: string(jose.RS256),
Use: "sig",
KeyID: fmt.Sprint(id),
},
},
}); err != nil {
return tsweb.Error(500, err.Error(), err)
}
return nil
}
// openIDProviderMetadata is a partial representation of
// https://openid.net/specs/openid-connect-discovery-1_0.html#ProviderMetadata.
type openIDProviderMetadata struct {
Issuer string `json:"issuer"`
AuthorizationEndpoint string `json:"authorization_endpoint,omitempty"`
UserInfoEndpoint string `json:"userinfo_endpoint,omitempty"`
JWKS_URI string `json:"jwks_uri"`
ScopesSupported views.Slice[string] `json:"scopes_supported"`
ResponseTypesSupported views.Slice[string] `json:"response_types_supported"`
SubjectTypesSupported views.Slice[string] `json:"subject_types_supported"`
ClaimsSupported views.Slice[string] `json:"claims_supported"`
IDTokenSigningAlgValuesSupported views.Slice[string] `json:"id_token_signing_alg_values_supported"`
// TODO(maisem): maybe add other fields?
// Currently we fill out the REQUIRED fields, scopes_supported and claims_supported.
}
type tailscaleClaims struct {
jwt.Claims `json:",inline"`
Key key.NodePublic `json:"key"` // the node public key
Addresses views.Slice[netip.Prefix] `json:"addresses"` // the Tailscale IPs of the node
NodeID tailcfg.NodeID `json:"nid"` // the stable node ID
NodeName string `json:"node"` // name of the node
Tailnet string `json:"tailnet"` // tailnet (like tail-scale.ts.net)
// Tags is the list of tags the node is tagged with prefixed with the Tailnet name.
Tags []string `json:"tags,omitempty"` // the tags on the node (like alice.github:tag:foo or example.com:tag:foo)
// User is the emailish of the user prefixed with the Tailnet name.
User string `json:"user,omitempty"` // user emailish (like alice.github:alice@github or example.com:bob@example.com)
UserID tailcfg.UserID `json:"uid,omitempty"` // user legacy id
}
var (
openIDSupportedClaims = views.SliceOf([]string{
// Standard claims, these correspond to fields in jwt.Claims.
"sub", "aud", "exp", "iat", "iss", "jti", "nbf",
// Tailscale claims, these correspond to fields in tailscaleClaims.
"key", "addresses", "nid", "node", "tailnet", "tags", "user", "uid",
})
// As defined in the OpenID spec this should be "openid".
openIDSupportedScopes = views.SliceOf([]string{"openid", "email", "profile"})
// We only support getting the id_token.
openIDSupportedReponseTypes = views.SliceOf([]string{"id_token", "code"})
// The type of the "sub" field in the JWT, which means it is globally unique identifier.
// The other option is "pairwise", which means the identifier is different per receiving 3p.
openIDSupportedSubjectTypes = views.SliceOf([]string{"public"})
// The algo used for signing. The OpenID spec says "The algorithm RS256 MUST be included."
// https://openid.net/specs/openid-connect-discovery-1_0.html#ProviderMetadata
openIDSupportedSigningAlgos = views.SliceOf([]string{string(jose.RS256)})
)
func (s *idpServer) serveOpenIDConfig(w http.ResponseWriter, r *http.Request) error {
if r.URL.Path != oidcConfigPath {
return tsweb.Error(404, "", nil)
}
w.Header().Set("Content-Type", "application/json")
if err := json.NewEncoder(io.MultiWriter(w, os.Stderr)).Encode(openIDProviderMetadata{
Issuer: s.serverURL + "/",
JWKS_URI: s.serverURL + oidcJWKSPath,
UserInfoEndpoint: s.serverURL + "/userinfo",
AuthorizationEndpoint: s.serverURL + "/authorize", // TODO: add / suffix
ScopesSupported: openIDSupportedScopes,
ResponseTypesSupported: openIDSupportedReponseTypes,
SubjectTypesSupported: openIDSupportedSubjectTypes,
ClaimsSupported: openIDSupportedClaims,
IDTokenSigningAlgValuesSupported: openIDSupportedSigningAlgos,
}); err != nil {
log.Printf("Error encoding JSON: %v", err)
http.Error(w, err.Error(), http.StatusInternalServerError)
}
return nil
}
const (
minimumRSAKeySize = 2048
)
// mustGenRSAKey generates a new RSA key with the provided number of bits. It
// panics on failure. bits must be at least minimumRSAKeySizeBytes * 8.
func mustGenRSAKey(bits int) (kid uint64, k *rsa.PrivateKey) {
if bits < minimumRSAKeySize {
panic("request to generate a too-small RSA key")
}
kid = must.Get(readUint64(crand.Reader))
k = must.Get(rsa.GenerateKey(crand.Reader, bits))
return
}
// readUint64 reads from r until 8 bytes represent a non-zero uint64.
func readUint64(r io.Reader) (uint64, error) {
for {
var b [8]byte
if _, err := io.ReadFull(r, b[:]); err != nil {
return 0, err
}
if v := binary.BigEndian.Uint64(b[:]); v != 0 {
return v, nil
}
}
}
// rsaPrivateKeyJSONWrapper is the the JSON serialization
// format used by RSAPrivateKey.
type rsaPrivateKeyJSONWrapper struct {
Key string
ID uint64
}
func marshalKeyJSON(k *rsa.PrivateKey, kid uint64) ([]byte, error) {
b := pem.Block{
Type: "RSA PRIVATE KEY",
Bytes: x509.MarshalPKCS1PrivateKey(k),
}
bts := pem.EncodeToMemory(&b)
return json.Marshal(rsaPrivateKeyJSONWrapper{
Key: base64.URLEncoding.EncodeToString(bts),
ID: kid,
})
}
func unmarshalKeyJSON(b []byte) (*rsa.PrivateKey, uint64, error) {
var wrapper rsaPrivateKeyJSONWrapper
if err := json.Unmarshal(b, &wrapper); err != nil {
return nil, 0, err
}
if len(wrapper.Key) == 0 {
return nil, 0, nil
}
b64dec, err := base64.URLEncoding.DecodeString(wrapper.Key)
if err != nil {
return nil, 0, err
}
blk, _ := pem.Decode(b64dec)
k, err := x509.ParsePKCS1PrivateKey(blk.Bytes)
return k, wrapper.ID, err
}