Initial commit

client/keys.go

+package main
+
+import (
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/rsa"
+	"fmt"
+
+	"golang.org/x/crypto/ssh"
+)
+
+const (
+	rsaKey   = "rsa"
+	ecdsaKey = "ecdsa"
+)
+
+type key interface{}
+
+func generateRSAKey(bits int) (*rsa.PrivateKey, ssh.PublicKey, error) {
+	k, err := rsa.GenerateKey(rand.Reader, bits)
+	if err != nil {
+		return nil, nil, err
+	}
+	pub, err := ssh.NewPublicKey(&k.PublicKey)
+	if err != nil {
+		return nil, nil, err
+	}
+	return k, pub, nil
+}
+
+func generateECDSAKey(bits int) (*ecdsa.PrivateKey, ssh.PublicKey, error) {
+	var curve elliptic.Curve
+	switch bits {
+	case 256:
+		curve = elliptic.P256()
+	case 384:
+		curve = elliptic.P384()
+	case 521:
+		curve = elliptic.P521()
+	default:
+		return nil, nil, fmt.Errorf("Unsupported key size. Valid sizes are '256', '384', '521'")
+	}
+	k, err := ecdsa.GenerateKey(curve, rand.Reader)
+	if err != nil {
+		return nil, nil, err
+	}
+	pub, err := ssh.NewPublicKey(&k.PublicKey)
+	if err != nil {
+		return nil, nil, err
+	}
+	return k, pub, nil
+}
+
+func generateKey(keytype string, bits int) (key, ssh.PublicKey, error) {
+	switch keytype {
+	case rsaKey:
+		return generateRSAKey(bits)
+	case ecdsaKey:
+		return generateECDSAKey(bits)
+	default:
+		return nil, nil, fmt.Errorf("Unsupported key type %s. Valid choices are [%s, %s]", keytype, rsaKey, ecdsaKey)
+	}
+}

client/main.go

+package main
+
+import (
+	"bytes"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"net"
+	"net/http"
+	"os"
+	"time"
+
+	"github.com/nsheridan/cashier/lib"
+	"golang.org/x/crypto/ssh"
+	"golang.org/x/crypto/ssh/agent"
+)
+
+var (
+	url      = flag.String("url", "http://localhost:10000/sign", "Signing URL")
+	keybits  = flag.Int("bits", 4096, "Key size")
+	validity = flag.Duration("validity", time.Hour*24, "Key validity")
+	keytype  = flag.String("key_type", "rsa", "Type of private key to generate - rsa or ecdsa")
+)
+
+func installCert(a agent.Agent, cert *ssh.Certificate, key key) error {
+	pubcert := agent.AddedKey{
+		PrivateKey:  key,
+		Certificate: cert,
+		Comment:     cert.KeyId,
+	}
+	if err := a.Add(pubcert); err != nil {
+		return fmt.Errorf("error importing certificate: %s", err)
+	}
+	return nil
+}
+
+func send(s []byte, token string) (*lib.SignResponse, error) {
+	req, err := http.NewRequest("POST", *url, bytes.NewReader(s))
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Add("Accept", "application/json")
+	req.Header.Set("Authorization", fmt.Sprintf("Bearer %s", token))
+	client := &http.Client{}
+	resp, err := client.Do(req)
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("Bad response from server: %s", resp.Status)
+	}
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	body, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+	c := &lib.SignResponse{}
+	if err := json.Unmarshal(body, c); err != nil {
+		return nil, err
+	}
+	return c, nil
+}
+
+func sign(pub ssh.PublicKey, token string) (*ssh.Certificate, error) {
+	marshaled := ssh.MarshalAuthorizedKey(pub)
+	marshaled = marshaled[:len(marshaled)-1]
+	s, err := json.Marshal(&lib.SignRequest{
+		Key:        string(marshaled),
+		ValidUntil: time.Now().Add(*validity),
+	})
+	if err != nil {
+		return nil, err
+	}
+	resp, err := send(s, token)
+	if err != nil {
+		return nil, err
+	}
+	if resp.Status != "ok" {
+		return nil, fmt.Errorf("error: %s", resp.Response)
+	}
+	k, _, _, _, err := ssh.ParseAuthorizedKey([]byte(resp.Response))
+	if err != nil {
+		return nil, err
+	}
+	cert, ok := k.(*ssh.Certificate)
+	if !ok {
+		return nil, fmt.Errorf("did not receive a certificate from server")
+	}
+	return cert, nil
+}
+
+func main() {
+	flag.Parse()
+
+	priv, pub, err := generateKey(*keytype, *keybits)
+	if err != nil {
+		log.Fatalln("Error generating key pair: ", err)
+	}
+
+	fmt.Print("Enter token: ")
+	var token string
+	fmt.Scanln(&token)
+
+	cert, err := sign(pub, token)
+	if err != nil {
+		log.Fatalln(err)
+	}
+	sock, err := net.Dial("unix", os.Getenv("SSH_AUTH_SOCK"))
+	if err != nil {
+		log.Fatalln("Error connecting to agent: %s", err)
+	}
+	defer sock.Close()
+	a := agent.NewClient(sock)
+	if err := installCert(a, cert, priv); err != nil {
+		log.Fatalln(err)
+	}
+	fmt.Println("Certificate added.")
+}

exampleconfig.json

+{
+  "server": {
+    "tls_key": "server.key",
+    "tls_cert": "server.crt",
+    "port": 443,
+    "cookie_secret": "supersecret"
+  },
+  "auth": {
+    "provider": "google",
+    "oauth_client_id": "nnnnnnnnnnnnnnnn.apps.googleusercontent.com",
+    "oauth_client_secret": "yyyyyyyyyyyyyyyyyyyyyy",
+    "oauth_callback_url": "https://sshca.example.com/auth/callback",
+    "google_opts": {
+      "domain": "example.com"
+    },
+    "jwt_signing_key": "supersecret"
+  },
+  "ssh": {
+    "signing_key": "signing_key",
+    "additional_principals": ["ec2-user"],
+    "max_age": "720h",
+    "permissions": ["permit-pty"]
+  }
+}

lib/const.go

+package lib
+
+import "time"
+
+// SignRequest represents a signing request sent to the server.
+type SignRequest struct {
+	Key        string    `json:"key"`
+	Principal  string    `json:"principal"`
+	ValidUntil time.Time `json:"valid_until"`
+}
+
+// SignResponse is sent by the server.
+// `Status' is "ok" or "error".
+// `Response' contains a signed certificate or an error message.
+type SignResponse struct {
+	Status   string `json:"status"`
+	Response string `json:"response"`
+}

server/auth/google/google.go

+package google
+
+import (
+	"fmt"
+	"net/http"
+	"strings"
+
+	"github.com/nsheridan/cashier/server/auth"
+	"github.com/nsheridan/cashier/server/config"
+
+	"golang.org/x/oauth2"
+	"golang.org/x/oauth2/google"
+	googleapi "google.golang.org/api/oauth2/v2"
+)
+
+const (
+	revokeURL = "https://accounts.google.com/o/oauth2/revoke?token=%s"
+	name      = "google"
+)
+
+type Config struct {
+	config *oauth2.Config
+	domain string
+}
+
+func New(c config.Auth) auth.Provider {
+	return &Config{
+		config: &oauth2.Config{
+			ClientID:     c.OauthClientID,
+			ClientSecret: c.OauthClientSecret,
+			RedirectURL:  c.OauthCallbackURL,
+			Endpoint:     google.Endpoint,
+			Scopes:       []string{googleapi.UserinfoEmailScope, googleapi.UserinfoProfileScope},
+		},
+		domain: c.GoogleOpts["domain"].(string),
+	}
+}
+
+func (c *Config) newClient(token *oauth2.Token) *http.Client {
+	return c.config.Client(oauth2.NoContext, token)
+}
+
+func (c *Config) Name() string {
+	return name
+}
+
+func (c *Config) Valid(token *oauth2.Token) bool {
+	if !token.Valid() {
+		return false
+	}
+	svc, err := googleapi.New(c.newClient(token))
+	if err != nil {
+		return false
+	}
+	t := svc.Tokeninfo()
+	t.AccessToken(token.AccessToken)
+	ti, err := t.Do()
+	if err != nil {
+		return false
+	}
+	ui, err := svc.Userinfo.Get().Do()
+	if err != nil {
+		return false
+	}
+	switch {
+	case ti.Audience != c.config.ClientID:
+	case ui.Hd != c.domain:
+		return false
+	}
+	return true
+}
+
+func (c *Config) Revoke(token *oauth2.Token) error {
+	h := c.newClient(token)
+	_, err := h.Get(fmt.Sprintf(revokeURL, token.AccessToken))
+	return err
+}
+
+func (c *Config) StartSession(state string) *auth.Session {
+	return &auth.Session{
+		AuthURL: c.config.AuthCodeURL(state, oauth2.SetAuthURLParam("hd", c.domain)),
+		State:   state,
+	}
+}
+
+func (c *Config) Exchange(code string) (*oauth2.Token, error) {
+	return c.config.Exchange(oauth2.NoContext, code)
+}
+
+func (c *Config) Username(token *oauth2.Token) string {
+	svc, err := googleapi.New(c.newClient(token))
+	if err != nil {
+		return ""
+	}
+	ui, err := svc.Userinfo.Get().Do()
+	if err != nil {
+		return ""
+	}
+	return strings.Split(ui.Email, "@")[0]
+}

server/auth/provider.go

+package auth
+
+import "golang.org/x/oauth2"
+
+type Provider interface {
+	Name() string
+	StartSession(string) *Session
+	Exchange(string) (*oauth2.Token, error)
+	Username(*oauth2.Token) string
+	Valid(*oauth2.Token) bool
+	Revoke(*oauth2.Token) error
+}
+
+type Session struct {
+	AuthURL string
+	Token   *oauth2.Token
+	State   string
+}
+
+func (s *Session) Authorize(provider Provider, code string) error {
+	t, err := provider.Exchange(code)
+	if err != nil {
+		return err
+	}
+	s.Token = t
+	return nil
+}

server/config/config.go

+package config
+
+import "github.com/spf13/viper"
+
+// Config holds the values from the json config file.
+type Config struct {
+	Server Server `mapstructure:"server"`
+	Auth   Auth   `mapstructure:"auth"`
+	SSH    SSH    `mapstructure:"ssh"`
+}
+
+// Server holds the configuration specific to the web server and sessions.
+type Server struct {
+	UseTLS       bool   `mapstructure:"use_tls"`
+	TLSKey       string `mapstructure:"tls_key"`
+	TLSCert      string `mapstructure:"tls_cert"`
+	Port         int    `mapstructure:"port"`
+	CookieSecret string `mapstructure:"cookie_secret"`
+}
+
+// Auth holds the configuration specific to the OAuth provider.
+type Auth struct {
+	OauthClientID     string                 `mapstructure:"oauth_client_id"`
+	OauthClientSecret string                 `mapstructure:"oauth_client_secret"`
+	OauthCallbackURL  string                 `mapstructure:"oauth_callback_url"`
+	Provider          string                 `mapstructure:"provider"`
+	GoogleOpts        map[string]interface{} `mapstructure:"google_opts"`
+	JWTSigningKey     string                 `mapstructure:"jwt_signing_key"`
+}
+
+// SSH holds the configuration specific to signing ssh keys.
+type SSH struct {
+	SigningKey  string   `mapstructure:"signing_key"`
+	Principals  []string `mapstructure:"principals"`
+	MaxAge      string   `mapstructure:"max_age"`
+	Permissions []string `mapstructure:"permissions"`
+}
+
+// ReadConfig parses a JSON configuration file into a Config struct.
+func ReadConfig(filename string) (*Config, error) {
+	config := &Config{}
+	v := viper.New()
+	v.SetConfigFile(filename)
+	if err := v.ReadInConfig(); err != nil {
+		return nil, err
+	}
+	if err := v.Unmarshal(config); err != nil {
+		return nil, err
+	}
+	return config, nil
+}

server/main.go

+package main
+
+import (
+	"crypto/rand"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"flag"
+	"fmt"
+	"html/template"
+	"io"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"time"
+
+	"golang.org/x/oauth2"
+
+	"github.com/dgrijalva/jwt-go"
+	"github.com/gorilla/mux"
+	"github.com/gorilla/sessions"
+	"github.com/nsheridan/cashier/lib"
+	"github.com/nsheridan/cashier/server/auth"
+	"github.com/nsheridan/cashier/server/auth/google"
+	"github.com/nsheridan/cashier/server/config"
+	"github.com/nsheridan/cashier/server/signer"
+)
+
+var (
+	cfg = flag.String("config_file", "config.json", "Path to configuration file.")
+)
+
+type appContext struct {
+	cookiestore   *sessions.CookieStore
+	authprovider  auth.Provider
+	authsession   *auth.Session
+	views         *template.Template
+	sshKeySigner  *signer.KeySigner
+	jwtSigningKey []byte
+}
+
+func (a *appContext) getAuthCookie(r *http.Request) *oauth2.Token {
+	session, _ := a.cookiestore.Get(r, "tok")
+	t, ok := session.Values["token"]
+	if !ok {
+		return nil
+	}
+	var tok oauth2.Token
+	if err := json.Unmarshal(t.([]byte), &tok); err != nil {
+		return nil
+	}
+	if !a.authprovider.Valid(&tok) {
+		return nil
+	}
+	return &tok
+}
+
+func (a *appContext) setAuthCookie(w http.ResponseWriter, r *http.Request, t *oauth2.Token) {
+	session, _ := a.cookiestore.Get(r, "tok")
+	val, _ := json.Marshal(t)
+	session.Values["token"] = val
+	session.Save(r, w)
+}
+
+func parseKey(r *http.Request) (*lib.SignRequest, error) {
+	var s lib.SignRequest
+	body, err := ioutil.ReadAll(r.Body)
+	if err != nil {
+		return nil, err
+	}
+	if err := json.Unmarshal(body, &s); err != nil {
+		return nil, err
+	}
+	return &s, nil
+}
+func signHandler(a *appContext, w http.ResponseWriter, r *http.Request) (int, error) {
+	jwtoken, err := jwt.ParseFromRequest(r, func(t *jwt.Token) (interface{}, error) {
+		return a.jwtSigningKey, nil
+	})
+	if err != nil {
+		return http.StatusUnauthorized, errors.New(http.StatusText(http.StatusUnauthorized))
+	}
+	if !jwtoken.Valid {
+		log.Printf("Token %v not valid", jwtoken)
+		return http.StatusUnauthorized, errors.New(http.StatusText(http.StatusUnauthorized))
+	}
+	expiry := int64(jwtoken.Claims["exp"].(float64))
+	token := &oauth2.Token{
+		AccessToken: jwtoken.Claims["token"].(string),
+		Expiry:      time.Unix(expiry, 0),
+	}
+	ok := a.authprovider.Valid(token)
+	if !ok {
+		return http.StatusUnauthorized, errors.New(http.StatusText(http.StatusUnauthorized))
+	}
+	// finally sign the pubkey and issue the cert.
+	req, err := parseKey(r)
+	req.Principal = a.authprovider.Username(token)
+	if err != nil {
+		return http.StatusInternalServerError, err
+	}
+	signed, err := a.sshKeySigner.Sign(req)
+	a.authprovider.Revoke(token)
+	if err != nil {
+		return http.StatusInternalServerError, err
+	}
+	json.NewEncoder(w).Encode(&lib.SignResponse{
+		Status:   "ok",
+		Response: signed,
+	})
+	return http.StatusOK, nil
+}
+
+func loginHandler(a *appContext, w http.ResponseWriter, r *http.Request) (int, error) {
+	a.authsession = a.authprovider.StartSession(hex.EncodeToString(random(32)))
+	http.Redirect(w, r, a.authsession.AuthURL, http.StatusFound)
+	return http.StatusFound, nil
+}
+
+func callbackHandler(a *appContext, w http.ResponseWriter, r *http.Request) (int, error) {
+	if r.FormValue("state") != a.authsession.State {
+		return http.StatusUnauthorized, errors.New(http.StatusText(http.StatusUnauthorized))
+	}
+	code := r.FormValue("code")
+	if err := a.authsession.Authorize(a.authprovider, code); err != nil {
+		return http.StatusInternalServerError, err
+	}
+	a.setAuthCookie(w, r, a.authsession.Token)
+	http.Redirect(w, r, "/", http.StatusFound)
+	return http.StatusFound, nil
+}
+
+func rootHandler(a *appContext, w http.ResponseWriter, r *http.Request) (int, error) {
+	tok := a.getAuthCookie(r)
+	if !tok.Valid() {
+		http.Redirect(w, r, "/auth/login", http.StatusSeeOther)
+		return http.StatusSeeOther, nil
+	}
+	j := jwt.New(jwt.SigningMethodHS256)
+	j.Claims["token"] = tok.AccessToken
+	j.Claims["exp"] = tok.Expiry.Unix()
+	t, err := j.SignedString(a.jwtSigningKey)
+	if err != nil {
+		return http.StatusInternalServerError, err
+	}
+	page := struct {
+		Token string
+	}{t}
+	a.views.ExecuteTemplate(w, "token.html", page)
+	return http.StatusOK, nil
+}
+
+type appHandler struct {
+	*appContext
+	h func(*appContext, http.ResponseWriter, *http.Request) (int, error)
+}
+
+func (ah appHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	status, err := ah.h(ah.appContext, w, r)
+	if err != nil {
+		log.Printf("HTTP %d: %q", status, err)
+		switch status {
+		case http.StatusNotFound:
+			http.NotFound(w, r)
+		case http.StatusInternalServerError:
+			http.Error(w, http.StatusText(status), status)
+		default:
+			http.Error(w, http.StatusText(status), status)
+		}
+	}
+}
+
+func random(length int) []byte {
+	k := make([]byte, length)
+	if _, err := io.ReadFull(rand.Reader, k); err != nil {
+		return nil
+	}
+	return k
+}
+
+func main() {
+	flag.Parse()
+	config, err := config.ReadConfig(*cfg)
+	if err != nil {
+		log.Fatal(err)
+	}
+	signer, err := signer.NewSigner(config.SSH)
+	if err != nil {
+		log.Fatal(err)
+	}
+	authprovider := google.New(config.Auth)
+	ctx := &appContext{
+		cookiestore:   sessions.NewCookieStore([]byte(config.Server.CookieSecret)),
+		authprovider:  authprovider,
+		views:         template.Must(template.ParseGlob("templates/*")),
+		sshKeySigner:  signer,
+		jwtSigningKey: []byte(config.Auth.JWTSigningKey),
+	}
+	ctx.cookiestore.Options = &sessions.Options{
+		MaxAge:   900,
+		Path:     "/",
+		Secure:   config.Server.UseTLS,
+		HttpOnly: true,
+	}
+
+	m := mux.NewRouter()
+	m.Handle("/", appHandler{ctx, rootHandler})
+	m.Handle("/auth/login", appHandler{ctx, loginHandler})
+	m.Handle("/auth/callback", appHandler{ctx, callbackHandler})
+	m.Handle("/sign", appHandler{ctx, signHandler})
+
+	fmt.Println("Starting server...")
+	l := fmt.Sprintf(":%d", config.Server.Port)
+	if config.Server.UseTLS {
+		log.Fatal(http.ListenAndServeTLS(l, config.Server.TLSCert, config.Server.TLSKey, m))
+	}
+	log.Fatal(http.ListenAndServe(l, m))
+}

server/signer/signer.go

+package signer
+
+import (
+	"crypto/rand"
+	"fmt"
+	"io/ioutil"
+	"time"
+
+	"github.com/nsheridan/cashier/lib"
+	"github.com/nsheridan/cashier/server/config"
+	"golang.org/x/crypto/ssh"
+)
+
+type KeySigner struct {
+	ca          ssh.Signer
+	validity    time.Duration
+	principals  []string
+	permissions map[string]string
+}
+
+func (s *KeySigner) Sign(req *lib.SignRequest) (string, error) {
+	pubkey, _, _, _, err := ssh.ParseAuthorizedKey([]byte(req.Key))
+	if err != nil {
+		return "", err
+	}
+	expires := time.Now().Add(s.validity)
+	if req.ValidUntil.After(expires) {
+		req.ValidUntil = expires
+	}
+	cert := &ssh.Certificate{
+		CertType:    ssh.UserCert,
+		Key:         pubkey,
+		KeyId:       req.Principal,
+		ValidBefore: uint64(req.ValidUntil.Unix()),
+		ValidAfter:  uint64(time.Now().Add(-5 * time.Minute).Unix()),
+	}
+	cert.ValidPrincipals = append(cert.ValidPrincipals, req.Principal)
+	cert.ValidPrincipals = append(cert.ValidPrincipals, s.principals...)
+	cert.Extensions = s.permissions
+	if err := cert.SignCert(rand.Reader, s.ca); err != nil {
+		return "", err
+	}
+	marshaled := ssh.MarshalAuthorizedKey(cert)
+	// Remove the trailing newline.
+	marshaled = marshaled[:len(marshaled)-1]
+	return string(marshaled), nil
+}
+
+func makeperms(perms []string) map[string]string {
+	if len(perms) > 0 {
+		m := make(map[string]string)
+		for _, p := range perms {
+			m[p] = ""
+		}
+		return m
+	}
+	return map[string]string{
+		"permit-X11-forwarding":   "",
+		"permit-agent-forwarding": "",
+		"permit-port-forwarding":  "",
+		"permit-pty":              "",
+		"permit-user-rc":          "",
+	}
+}
+
+func NewSigner(conf config.SSH) (*KeySigner, error) {
+	data, err := ioutil.ReadFile(conf.SigningKey)
+	if err != nil {
+		return nil, fmt.Errorf("unable to read CA key %s: %v", conf.SigningKey, err)
+	}
+	key, err := ssh.ParsePrivateKey(data)
+	if err != nil {
+		return nil, fmt.Errorf("unable to parse CA key: %v", err)
+	}
+	validity, err := time.ParseDuration(conf.MaxAge)
+	if err != nil {
+		return nil, fmt.Errorf("error parsing duration '%s': %v", conf.MaxAge, err)
+	}
+	return &KeySigner{
+		ca:          key,
+		validity:    validity,
+		principals:  conf.Principals,
+		permissions: makeperms(conf.Permissions),
+	}, nil
+}

templates/token.html

+<html>
+  <head>
+    <title>YOUR TOKEN!</title>
+    <style>
+      <!--
+      body {
+        text-align: center;
+        font-family: sans-serif;
+        background-color: #edece4;
+        margin-top: 120px;
+      }
+      .code {
+        background-color: #26292B;
+        border: none;
+        color: #fff;
+        font-family: monospace;
+        font-size: 13;
+        font-weight: bold;
+        height: auto;
+        margin: 12px 12px 12px 12px;
+        padding: 12px 12px 12px 12px;
+        resize: none;
+        text-align: center;
+        width: 960px;
+      }
+      ::selection {
+        background: #32d0ff;
+        color: #000;
+      }
+      ::-moz-selection {
+        background: #32d0ff;
+        color: #000;
+      }
+      -->
+    </style>
+  </head>
+  <body>
+    <h2>
+      This is your token. There are many like it but this one is yours.
+    </h2>
+    <textarea class="code" readonly spellcheck="false" onclick="this.focus();this.select();">{{.Token}}</textarea>
+    <h2>
+      The token will expire in &lt; 1 hour.
+    </h2>
+  </body>
+</html>