// 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" "net/url" "os" "strings" "sync" "time" "gopkg.in/square/go-jose.v2" "gopkg.in/square/go-jose.v2/jwt" "tailscale.com/client/tailscale" "tailscale.com/client/tailscale/apitype" "tailscale.com/tailcfg" "tailscale.com/tsnet" "tailscale.com/types/key" "tailscale.com/types/lazy" "tailscale.com/types/logger" "tailscale.com/types/views" "tailscale.com/util/mak" "tailscale.com/util/must" "tailscale.com/util/rands" ) 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" lazyMux lazy.SyncValue[*http.ServeMux] lazySigningKey lazy.SyncValue[*signingKey] lazySigner lazy.SyncValue[jose.Signer] mu sync.Mutex // guards the fields below code map[string]*authRequest accessToken map[string]*authRequest } type authRequest struct { // requesterNodeID is the node who requested the auth (say synology), not the node // who is being authenticated. // String form of tailcfg.NodeID requesterNodeID string // nonce presented in the request. nonce string // redirectURI is the redirect_uri presented in the request. redirectURI string // remoteUser is the user who is being authenticated. remoteUser *apitype.WhoIsResponse // validTill is the time until which the token is valid. // As of 2023-11-14, it is 5 minutes. // TODO: add routine to delete expired tokens. validTill time.Time } func (s *idpServer) authorize(w http.ResponseWriter, r *http.Request) { who, err := s.lc.WhoIs(r.Context(), r.RemoteAddr) if err != nil { log.Printf("Error getting WhoIs: %v", err) http.Error(w, err.Error(), http.StatusInternalServerError) return } nodeID := strings.TrimPrefix(r.URL.Path, "/authorize/") uq := r.URL.Query() code := rands.HexString(32) ar := &authRequest{ requesterNodeID: nodeID, nonce: uq.Get("nonce"), remoteUser: who, redirectURI: uq.Get("redirect_uri"), } s.mu.Lock() mak.Set(&s.code, code, ar) s.mu.Unlock() q := make(url.Values) q.Set("code", code) q.Set("state", uq.Get("state")) u := uq.Get("redirect_uri") + "?" + q.Encode() log.Printf("Redirecting to %q", u) http.Redirect(w, r, u, http.StatusFound) } func (s *idpServer) newMux() *http.ServeMux { mux := http.NewServeMux() mux.HandleFunc(oidcJWKSPath, s.serveJWKS) mux.HandleFunc(oidcConfigPath, s.serveOpenIDConfig) mux.HandleFunc("/authorize/", s.authorize) mux.HandleFunc("/userinfo", s.serveUserInfo) mux.HandleFunc("/token", s.serveToken) mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) { if r.URL.Path == "/" { io.WriteString(w, "

Tailscale OIDC IdP

") return } http.Error(w, "tsidp: not found", http.StatusNotFound) }) return mux } func (s *idpServer) ServeHTTP(w http.ResponseWriter, r *http.Request) { log.Printf("%v %v", r.Method, r.URL) s.lazyMux.Get(s.newMux).ServeHTTP(w, r) } func (s *idpServer) serveUserInfo(w http.ResponseWriter, r *http.Request) { if r.Method != "GET" { http.Error(w, "tsidp: method not allowed", http.StatusMethodNotAllowed) return } tk, ok := strings.CutPrefix(r.Header.Get("Authorization"), "Bearer ") if !ok { http.Error(w, "tsidp: invalid Authorization header", http.StatusBadRequest) return } who, err := s.lc.WhoIs(r.Context(), r.RemoteAddr) if err != nil { log.Printf("Error getting WhoIs: %v", err) http.Error(w, err.Error(), http.StatusInternalServerError) return } s.mu.Lock() ar, ok := s.accessToken[tk] s.mu.Unlock() if !ok { http.Error(w, "tsidp: invalid token", http.StatusBadRequest) return } if ar.requesterNodeID != who.Node.ID.String() { http.Error(w, "tsidp: token for different node", http.StatusForbidden) return } if ar.validTill.Before(time.Now()) { http.Error(w, "tsidp: token expired", http.StatusBadRequest) s.mu.Lock() delete(s.accessToken, tk) s.mu.Unlock() } ui := userInfo{} if ar.remoteUser.Node.IsTagged() { http.Error(w, "tsidp: tagged nodes not supported", http.StatusBadRequest) return } ui.Sub = ar.remoteUser.Node.User.String() ui.Name = ar.remoteUser.UserProfile.DisplayName ui.Email = ar.remoteUser.UserProfile.LoginName ui.Picture = ar.remoteUser.UserProfile.ProfilePicURL // TODO(maisem): not sure if this is the right thing to do ui.UserName, _, _ = strings.Cut(ar.remoteUser.UserProfile.LoginName, "@") w.Header().Set("Content-Type", "application/json") if err := json.NewEncoder(w).Encode(ui); err != nil { http.Error(w, err.Error(), http.StatusInternalServerError) } } type userInfo struct { Sub string `json:"sub"` Name string `json:"name"` Email string `json:"email"` Picture string `json:"picture"` UserName string `json:"username"` } func (s *idpServer) serveToken(w http.ResponseWriter, r *http.Request) { if r.Method != "POST" { http.Error(w, "tsidp: method not allowed", http.StatusMethodNotAllowed) return } caller, err := s.lc.WhoIs(r.Context(), r.RemoteAddr) if err != nil { log.Printf("Error getting WhoIs: %v", err) http.Error(w, err.Error(), http.StatusInternalServerError) return } if r.FormValue("grant_type") != "authorization_code" { http.Error(w, "tsidp: grant_type not supported", http.StatusBadRequest) return } code := r.FormValue("code") if code == "" { http.Error(w, "tsidp: code is required", http.StatusBadRequest) return } s.mu.Lock() ar, ok := s.code[code] delete(s.code, code) s.mu.Unlock() if !ok { http.Error(w, "tsidp: code not found", http.StatusBadRequest) return } if ar.requesterNodeID != caller.Node.ID.String() { http.Error(w, "tsidp: token for different node", http.StatusForbidden) return } if ar.redirectURI != r.FormValue("redirect_uri") { http.Error(w, "tsidp: redirect_uri mismatch", http.StatusBadRequest) return } signer, err := s.oidcSigner() if err != nil { log.Printf("Error getting signer: %v", err) http.Error(w, err.Error(), http.StatusInternalServerError) return } jti := rands.HexString(32) who := ar.remoteUser // TODO(maisem): not sure if this is the right thing to do userName, _, _ := strings.Cut(ar.remoteUser.UserProfile.LoginName, "@") n := who.Node.View() if n.IsTagged() { http.Error(w, "tsidp: tagged nodes not supported", http.StatusBadRequest) return } now := time.Now() _, tcd, _ := strings.Cut(n.Name(), ".") tsClaims := tailscaleClaims{ Claims: jwt.Claims{ Audience: jwt.Audience{"unused"}, Expiry: jwt.NewNumericDate(now.Add(5 * time.Minute)), ID: jti, IssuedAt: jwt.NewNumericDate(now), Issuer: s.serverURL, NotBefore: jwt.NewNumericDate(now), Subject: n.User().String(), }, Nonce: ar.nonce, Key: n.Key(), Addresses: n.Addresses(), NodeID: n.ID(), NodeName: n.Name(), Tailnet: tcd, UserID: n.User(), Email: who.UserProfile.LoginName, UserName: userName, } // Create an OIDC token using this issuer's signer. token, err := jwt.Signed(signer).Claims(tsClaims).CompactSerialize() if err != nil { log.Printf("Error getting token: %v", err) http.Error(w, err.Error(), http.StatusInternalServerError) return } at := rands.HexString(32) s.mu.Lock() ar.validTill = now.Add(5 * time.Minute) mak.Set(&s.accessToken, at, ar) s.mu.Unlock() w.Header().Set("Content-Type", "application/json") if err := json.NewEncoder(w).Encode(oidcTokenResponse{ AccessToken: at, TokenType: "Bearer", ExpiresIn: 5 * 60, IDToken: token, }); err != nil { http.Error(w, err.Error(), http.StatusInternalServerError) } } type oidcTokenResponse struct { IDToken string `json:"id_token"` TokenType string `json:"token_type"` AccessToken string `json:"access_token"` RefreshToken string `json:"refresh_token"` ExpiresIn int `json:"expires_in"` } const ( oidcJWKSPath = "/.well-known/jwks.json" oidcConfigPath = "/.well-known/openid-configuration" ) func (s *idpServer) oidcSigner() (jose.Signer, error) { return s.lazySigner.GetErr(func() (jose.Signer, error) { sk, err := s.oidcPrivateKey() if err != nil { return nil, err } return jose.NewSigner(jose.SigningKey{ Algorithm: jose.RS256, Key: sk.k, }, &jose.SignerOptions{EmbedJWK: false, ExtraHeaders: map[jose.HeaderKey]interface{}{ jose.HeaderType: "JWT", "kid": fmt.Sprint(sk.kid), }}) }) } func (s *idpServer) oidcPrivateKey() (*signingKey, error) { return s.lazySigningKey.GetErr(func() (*signingKey, error) { var sk signingKey b, err := os.ReadFile("oidc-key.json") if err == nil { if err := sk.UnmarshalJSON(b); err == nil { return &sk, nil } else { log.Printf("Error unmarshaling key: %v", err) } } id, k := mustGenRSAKey(2048) sk.k = k sk.kid = id b, err = sk.MarshalJSON() if err != nil { log.Fatalf("Error marshaling key: %v", err) } if err := os.WriteFile("oidc-key.json", b, 0600); err != nil { log.Fatalf("Error writing key: %v", err) } return &sk, nil }) } func (s *idpServer) serveJWKS(w http.ResponseWriter, r *http.Request) { if r.URL.Path != oidcJWKSPath { http.Error(w, "tsidp: not found", http.StatusNotFound) return } w.Header().Set("Content-Type", "application/json") sk, err := s.oidcPrivateKey() if err != nil { http.Error(w, err.Error(), http.StatusInternalServerError) return } // TODO(maisem): maybe only marshal this once and reuse? // TODO(maisem): implement key rotation. je := json.NewEncoder(w) je.SetIndent("", " ") if err := je.Encode(jose.JSONWebKeySet{ Keys: []jose.JSONWebKey{ { Key: sk.k.Public(), Algorithm: string(jose.RS256), Use: "sig", KeyID: fmt.Sprint(sk.kid), }, }, }); err != nil { http.Error(w, err.Error(), http.StatusInternalServerError) } return } // 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"` TokenEndpoint string `json:"token_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"` Nonce string `json:"nonce,omitempty"` // the nonce from the request 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) // Email is the emailish of the user prefixed with the Tailnet name. Email string `json:"email,omitempty"` // user emailish (like alice.github:alice@github or example.com:bob@example.com) UserID tailcfg.UserID `json:"uid,omitempty"` // user legacy id UserName string `json:"username,omitempty"` // user name } var ( openIDSupportedClaims = views.SliceOf([]string{ // Standard claims, these correspond to fields in jwt.Claims. "sub", "aud", "exp", "iat", "iss", "jti", "nbf", "username", "email", // 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) { if r.URL.Path != oidcConfigPath { http.Error(w, "tsidp: not found", http.StatusNotFound) return } who, err := s.lc.WhoIs(r.Context(), r.RemoteAddr) if err != nil { log.Printf("Error getting WhoIs: %v", err) http.Error(w, err.Error(), http.StatusInternalServerError) return } authorizeEndpoint := fmt.Sprintf("%s/authorize/%s", s.serverURL, who.Node.ID.String()) w.Header().Set("Content-Type", "application/json") je := json.NewEncoder(w) je.SetIndent("", " ") if err := je.Encode(openIDProviderMetadata{ Issuer: s.serverURL, JWKS_URI: s.serverURL + oidcJWKSPath, UserInfoEndpoint: s.serverURL + "/userinfo", AuthorizationEndpoint: authorizeEndpoint, TokenEndpoint: s.serverURL + "/token", ScopesSupported: openIDSupportedScopes, ResponseTypesSupported: openIDSupportedReponseTypes, SubjectTypesSupported: openIDSupportedSubjectTypes, ClaimsSupported: openIDSupportedClaims, IDTokenSigningAlgValuesSupported: openIDSupportedSigningAlgos, }); err != nil { http.Error(w, err.Error(), http.StatusInternalServerError) } } 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 } type signingKey struct { k *rsa.PrivateKey kid uint64 } func (sk *signingKey) MarshalJSON() ([]byte, error) { b := pem.Block{ Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(sk.k), } bts := pem.EncodeToMemory(&b) return json.Marshal(rsaPrivateKeyJSONWrapper{ Key: base64.URLEncoding.EncodeToString(bts), ID: sk.kid, }) } func (sk *signingKey) UnmarshalJSON(b []byte) error { var wrapper rsaPrivateKeyJSONWrapper if err := json.Unmarshal(b, &wrapper); err != nil { return err } if len(wrapper.Key) == 0 { return nil } b64dec, err := base64.URLEncoding.DecodeString(wrapper.Key) if err != nil { return err } blk, _ := pem.Decode(b64dec) k, err := x509.ParsePKCS1PrivateKey(blk.Bytes) if err != nil { return err } sk.k = k sk.kid = wrapper.ID return nil }