oidc authentication: email_verified claim is not required for JWT validation

staging/src/k8s.io/apiserver/plugin/pkg/authenticator/token/oidc/oidc.go

@@ -284,16 +284,20 @@ func (a *Authenticator) AuthenticateToken(token string) (user.Info, bool, error)
 	}
 
 	if a.usernameClaim == "email" {
-		// Check the email_verified claim to ensure the email is valid.
+		// If the email_verified claim is present, ensure the email is valid.
 		// https://openid.net/specs/openid-connect-core-1_0.html#StandardClaims
+		if hasEmailVerified := c.hasClaim("email_verified"); hasEmailVerified {
 			var emailVerified bool
 			if err := c.unmarshalClaim("email_verified", &emailVerified); err != nil {
 				return nil, false, fmt.Errorf("oidc: parse 'email_verified' claim: %v", err)
 			}
+
+			// If the email_verified claim is present we have to verify it is set to `true`.
 			if !emailVerified {
 				return nil, false, fmt.Errorf("oidc: email not verified")
 			}
 		}
+	}
 
 	if a.usernamePrefix != "" {
 		username = a.usernamePrefix + username
@@ -347,3 +351,10 @@ func (c claims) unmarshalClaim(name string, v interface{}) error {
 	}
 	return json.Unmarshal([]byte(val), v)
 }
+
+func (c claims) hasClaim(name string) bool {
+	if _, ok := c[name]; !ok {
+		return false
+	}
+	return true
+}

staging/src/k8s.io/apiserver/plugin/pkg/authenticator/token/oidc/oidc_test.go

@@ -287,7 +287,7 @@ func TestToken(t *testing.T) {
 			wantErr: true,
 		},
 		{
-			// If "email_verified" isn't present, assume false
+			// If "email_verified" isn't present, assume true
 			name: "no-email-verified-claim",
 			options: Options{
 				IssuerURL:     "https://auth.example.com",
@@ -305,6 +305,30 @@ func TestToken(t *testing.T) {
 				"email": "jane@example.com",
 				"exp": %d
 			}`, valid.Unix()),
+			want: &user.DefaultInfo{
+				Name: "jane@example.com",
+			},
+		},
+		{
+			name: "invalid-email-verified-claim",
+			options: Options{
+				IssuerURL:     "https://auth.example.com",
+				ClientID:      "my-client",
+				UsernameClaim: "email",
+				now:           func() time.Time { return now },
+			},
+			signingKey: loadRSAPrivKey(t, "testdata/rsa_1.pem", jose.RS256),
+			pubKeys: []*jose.JSONWebKey{
+				loadRSAKey(t, "testdata/rsa_1.pem", jose.RS256),
+			},
+			// string value for "email_verified"
+			claims: fmt.Sprintf(`{
+				"iss": "https://auth.example.com",
+				"aud": "my-client",
+				"email": "jane@example.com",
+				"email_verified": "false",
+				"exp": %d
+			}`, valid.Unix()),
 			wantErr: true,
 		},
 		{