ABC-132: sign error page parameters (#8197)

* sign error page parameters

* add comments

app/app.go

@@ -4,6 +4,7 @@
 package app
 
 import (
+	"crypto/ecdsa"
 	"html/template"
 	"net"
 	"net/http"
@@ -60,13 +61,14 @@ type App struct {
 
 	newStore func() store.Store
 
-	htmlTemplateWatcher *utils.HTMLTemplateWatcher
-	sessionCache        *utils.Cache
-	roles               map[string]*model.Role
-	configListenerId    string
-	licenseListenerId   string
-	disableConfigWatch  bool
-	configWatcher       *utils.ConfigWatcher
+	htmlTemplateWatcher  *utils.HTMLTemplateWatcher
+	sessionCache         *utils.Cache
+	roles                map[string]*model.Role
+	configListenerId     string
+	licenseListenerId    string
+	disableConfigWatch   bool
+	configWatcher        *utils.ConfigWatcher
+	asymmetricSigningKey *ecdsa.PrivateKey
 
 	pluginCommands     []*PluginCommand
 	pluginCommandsLock sync.RWMutex
@@ -139,6 +141,10 @@ func New(options ...Option) (*App, error) {
 	}
 
 	app.Srv.Store = app.newStore()
+	if err := app.ensureAsymmetricSigningKey(); err != nil {
+		return nil, errors.Wrapf(err, "unable to ensure asymmetric signing key")
+	}
+
 	app.initJobs()
 
 	app.initBuiltInPlugins()
@@ -448,5 +454,5 @@ func (a *App) Handle404(w http.ResponseWriter, r *http.Request) {
 
 	l4g.Debug("%v: code=404 ip=%v", r.URL.Path, utils.GetIpAddress(r))
 
-	utils.RenderWebError(err, w, r)
+	utils.RenderWebAppError(w, r, err, a.AsymmetricSigningKey())
 }

app/config.go

@@ -4,7 +4,12 @@
 package app
 
 import (
+	"crypto/ecdsa"
+	"crypto/elliptic"
 	"crypto/md5"
+	"crypto/rand"
+	"crypto/x509"
+	"encoding/base64"
 	"encoding/json"
 	"fmt"
 	"runtime/debug"
@@ -116,8 +121,91 @@ func (a *App) InvokeConfigListeners(old, current *model.Config) {
 	}
 }
 
+// EnsureAsymmetricSigningKey ensures that an asymmetric signing key exists and future calls to
+// AsymmetricSigningKey will always return a valid signing key.
+func (a *App) ensureAsymmetricSigningKey() error {
+	if a.asymmetricSigningKey != nil {
+		return nil
+	}
+
+	var key *model.SystemAsymmetricSigningKey
+
+	result := <-a.Srv.Store.System().GetByName(model.SYSTEM_ASYMMETRIC_SIGNING_KEY)
+	if result.Err == nil {
+		if err := json.Unmarshal([]byte(result.Data.(*model.System).Value), &key); err != nil {
+			return err
+		}
+	}
+
+	// If we don't already have a key, try to generate one.
+	if key == nil {
+		newECDSAKey, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+		if err != nil {
+			return err
+		}
+		newKey := &model.SystemAsymmetricSigningKey{
+			ECDSAKey: &model.SystemECDSAKey{
+				Curve: "P-256",
+				X:     newECDSAKey.X,
+				Y:     newECDSAKey.Y,
+				D:     newECDSAKey.D,
+			},
+		}
+		system := &model.System{
+			Name: model.SYSTEM_ASYMMETRIC_SIGNING_KEY,
+		}
+		v, err := json.Marshal(newKey)
+		if err != nil {
+			return err
+		}
+		system.Value = string(v)
+		if result = <-a.Srv.Store.System().Save(system); result.Err == nil {
+			// If we were able to save the key, use it, otherwise ignore the error.
+			key = newKey
+		}
+	}
+
+	// If we weren't able to save a new key above, another server must have beat us to it. Get the
+	// key from the database, and if that fails, error out.
+	if key == nil {
+		result := <-a.Srv.Store.System().GetByName(model.SYSTEM_ASYMMETRIC_SIGNING_KEY)
+		if result.Err != nil {
+			return result.Err
+		} else if err := json.Unmarshal([]byte(result.Data.(*model.System).Value), &key); err != nil {
+			return err
+		}
+	}
+
+	var curve elliptic.Curve
+	switch key.ECDSAKey.Curve {
+	case "P-256":
+		curve = elliptic.P256()
+	default:
+		return fmt.Errorf("unknown curve: " + key.ECDSAKey.Curve)
+	}
+	a.asymmetricSigningKey = &ecdsa.PrivateKey{
+		PublicKey: ecdsa.PublicKey{
+			Curve: curve,
+			X:     key.ECDSAKey.X,
+			Y:     key.ECDSAKey.Y,
+		},
+		D: key.ECDSAKey.D,
+	}
+	a.regenerateClientConfig()
+	return nil
+}
+
+// AsymmetricSigningKey will return a private key that can be used for asymmetric signing.
+func (a *App) AsymmetricSigningKey() *ecdsa.PrivateKey {
+	return a.asymmetricSigningKey
+}
+
 func (a *App) regenerateClientConfig() {
 	a.clientConfig = utils.GenerateClientConfig(a.Config(), a.DiagnosticId())
+	if key := a.AsymmetricSigningKey(); key != nil {
+		der, _ := x509.MarshalPKIXPublicKey(&key.PublicKey)
+		a.clientConfig["AsymmetricSigningPublicKey"] = base64.StdEncoding.EncodeToString(der)
+	}
 	clientConfigJSON, _ := json.Marshal(a.clientConfig)
 	a.clientConfigHash = fmt.Sprintf("%x", md5.Sum(clientConfigJSON))
 }

app/config_test.go

@@ -6,6 +6,8 @@ package app
 import (
 	"testing"
 
+	"github.com/stretchr/testify/assert"
+
 	"github.com/mattermost/mattermost-server/model"
 )
 
@@ -54,3 +56,10 @@ func TestConfigListener(t *testing.T) {
 		t.Fatal("listener 2 should've been called")
 	}
 }
+
+func TestAsymmetricSigningKey(t *testing.T) {
+	th := Setup().InitBasic()
+	defer th.TearDown()
+	assert.NotNil(t, th.App.AsymmetricSigningKey())
+	assert.NotEmpty(t, th.App.ClientConfig()["AsymmetricSigningPublicKey"])
+}