2 files changed, 228 insertions, 0 deletions
diff --git a/pkg/auth/auth.go b/pkg/auth/auth.go
new file mode 100644
index 000000000..bd542bc32
--- /dev/null
+++ b/pkg/auth/auth.go
@@ -0,0 +1,129 @@
+// Copyright 2021 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+// Relies on tokeninfo because it is properly documented:
+// https://developers.google.com/identity/protocols/oauth2/openid-connect#validatinganidtoken
+
+// The client
+// The VM that wants to invoke the API:
+// 1) Gets a token from the metainfo server with this http request:
+//      META=http://metadata.google.internal/computeMetadata/v1
+//      AUD=https://syzkaller.appspot.com/api
+//      curl -sH 'Metadata-Flavor: Google' \
+//           "$META/instance/service-accounts/default/identity?audience=$AUD"
+// 2) Invokes /api with header 'Authorization: Bearer <token>'
+//
+// The AppEngine api server:
+// 1) Receive the token, invokes this http request:
+//      curl -s "https://oauth2.googleapis.com/tokeninfo?id_token=<token>"
+// 2) Checks the resulting JSON having the expected audience and expiration.
+// 3) Looks up the permissions in the config using the value of sub.
+//
+// https://cloud.google.com/iap/docs/signed-headers-howto#retrieving_the_user_identity
+// from the IAP docs agrees to trust sub.
+
+// Package auth contains authentication related code supporting secret
+// passwords and oauth2 tokens on GCE.
+package auth
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"net/url"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/google/syzkaller/dashboard/dashapi"
+)
+
+const (
+	// The official google oauth2 endpoint.
+	GoogleTokenInfoEndpoint = "https://oauth2.googleapis.com/tokeninfo"
+	// Used in the config map as a prefix to distinguish auth identifiers from secret passwords
+	// (which contain arbitrary strings, that can't have this prefix).
+	OauthMagic = "OauthSubject:"
+)
+
+// Represent a verification backend.
+type Endpoint struct {
+	// URL supporting tokeninfo auth2 protocol.
+	url string
+	// TODO(blackgnezdo): cache tokens with a bit of care for concurrency.
+}
+
+func MakeEndpoint(u string) Endpoint {
+	return Endpoint{url: u}
+}
+
+// The JSON representation of JWT claims.
+type jwtClaimsParse struct {
+	Subject  string `json:"sub"`
+	Audience string `json:"aud"`
+	// The field in the JSON is a string but contains a UNIX time.
+	Expiration string `json:"exp"`
+}
+
+// The typed representation of JWT claims.
+type jwtClaims struct {
+	Subject  string
+	Audience string
+	// The app uses the typed value.
+	Expiration time.Time
+}
+
+func (auth *Endpoint) queryTokenInfo(tokenValue string) (*jwtClaims, error) {
+	resp, err := http.PostForm(auth.url, url.Values{"id_token": {tokenValue}})
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	body, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+	claims := new(jwtClaimsParse)
+	if err = json.Unmarshal(body, claims); err != nil {
+		return nil, err
+	}
+	expInt, err := strconv.ParseInt(claims.Expiration, 10, 64)
+	if err != nil {
+		return nil, err
+	}
+	r := jwtClaims{
+		Subject:    claims.Subject,
+		Audience:   claims.Audience,
+		Expiration: time.Unix(expInt, 0),
+	}
+	return &r, nil
+}
+
+// Returns the verified subject value based on the provided header
+// value or "" if it can't be determined. A valid result starts with
+// auth.OauthMagic. The now parameter is the current time to compare the
+// claims against. The authHeader is styled as is typical for HTTP headers
+// which carry the tokens prefixed by "Bearer " string.
+func (auth *Endpoint) DetermineAuthSubj(now time.Time, authHeader []string) (string, error) {
+	if len(authHeader) != 1 || !strings.HasPrefix(authHeader[0], "Bearer") {
+		// This is a normal case when the client uses a password.
+		return "", nil
+	}
+	// Values past this point are real authentication attempts. Whether
+	// or not they are valid is the question.
+	tokenValue := strings.TrimSpace(strings.TrimPrefix(authHeader[0], "Bearer"))
+	claims, err := auth.queryTokenInfo(tokenValue)
+	if err != nil {
+		return "", err
+	}
+	if claims.Audience != dashapi.DashboardAudience {
+		err := fmt.Errorf("unexpected audience %v %v", claims.Audience, claims)
+		return "", err
+	}
+	if claims.Expiration.Before(now) {
+		err := fmt.Errorf("token past expiration %v", claims.Expiration)
+		return "", err
+	}
+	return OauthMagic + claims.Subject, nil
+}
diff --git a/pkg/auth/auth_test.go b/pkg/auth/auth_test.go
new file mode 100644
index 000000000..13a9c5749
--- /dev/null
+++ b/pkg/auth/auth_test.go
@@ -0,0 +1,99 @@
+// Copyright 2021 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package auth
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/google/syzkaller/dashboard/dashapi"
+)
+
+func reponseFor(t *testing.T, claims jwtClaims) (*httptest.Server, Endpoint) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		bytes, err := json.Marshal(jwtClaimsParse{
+			Subject:    claims.Subject,
+			Audience:   claims.Audience,
+			Expiration: fmt.Sprint(claims.Expiration.Unix()),
+		})
+		if err != nil {
+			t.Fatalf("Marshal %v", err)
+		}
+		w.Header()["Content-Type"] = []string{"application/json"}
+		w.Write(bytes)
+	}))
+	return ts, MakeEndpoint(ts.URL)
+}
+
+func TestBearerValid(t *testing.T) {
+	tm := time.Now()
+	magic := "ValidSubj"
+	ts, dut := reponseFor(t, jwtClaims{
+		Subject:    magic,
+		Audience:   dashapi.DashboardAudience,
+		Expiration: tm.AddDate(0, 0, 1),
+	})
+	defer ts.Close()
+
+	got, err := dut.DetermineAuthSubj(tm, []string{"Bearer x"})
+	if err != nil {
+		t.Errorf("Unexpected error %v", err)
+	}
+	if !strings.HasSuffix(got, magic) {
+		t.Errorf("Wrong subj %v not suffix of %v", magic, got)
+	}
+}
+
+func TestBearerWrongAudience(t *testing.T) {
+	tm := time.Now()
+	ts, dut := reponseFor(t, jwtClaims{
+		Subject:    "irrelevant",
+		Expiration: tm.AddDate(0, 0, 1),
+		Audience:   "junk",
+	})
+	defer ts.Close()
+
+	_, err := dut.DetermineAuthSubj(tm, []string{"Bearer x"})
+	if !strings.HasPrefix(err.Error(), "unexpected audience") {
+		t.Fatalf("Unexpected error %v", err)
+	}
+}
+
+func TestBearerExpired(t *testing.T) {
+	tm := time.Now()
+	ts, dut := reponseFor(t, jwtClaims{
+		Subject:    "irrelevant",
+		Expiration: tm.AddDate(0, 0, -1),
+		Audience:   dashapi.DashboardAudience,
+	})
+	defer ts.Close()
+
+	_, err := dut.DetermineAuthSubj(tm, []string{"Bearer x"})
+	if !strings.HasPrefix(err.Error(), "token past expiration") {
+		t.Fatalf("Unexpected error %v", err)
+	}
+}
+
+func TestMissingHeader(t *testing.T) {
+	ts, dut := reponseFor(t, jwtClaims{})
+	defer ts.Close()
+	got, err := dut.DetermineAuthSubj(time.Now(), []string{})
+	if err != nil || got != "" {
+		t.Errorf("Unexpected error %v %v", got, err)
+	}
+}
+
+func TestBadHeader(t *testing.T) {
+	ts, dut := reponseFor(t, jwtClaims{})
+	defer ts.Close()
+	got, err := dut.DetermineAuthSubj(time.Now(), []string{"bad"})
+	if err != nil || got != "" {
+		t.Errorf("Unexpected error %v %v", got, err)
+	}
+}