feat(OP): add back channel logout support (#671)

* feat: add configuration support for back channel logout

* logout token

* indicate back channel logout support in discovery endpoint

pkg/oidc/discovery.go

@@ -145,6 +145,14 @@ type DiscoveryConfiguration struct {
 
 	// OPTermsOfServiceURI is a URL the OpenID Provider provides to the person registering the Client to read about OpenID Provider's terms of service.
 	OPTermsOfServiceURI string `json:"op_tos_uri,omitempty"`
+
+	// BackChannelLogoutSupported specifies whether the OP supports back-channel logout (https://openid.net/specs/openid-connect-backchannel-1_0.html),
+	// with true indicating support. If omitted, the default value is false.
+	BackChannelLogoutSupported bool `json:"backchannel_logout_supported,omitempty"`
+
+	// BackChannelLogoutSessionSupported specifies whether the OP can pass a sid (session ID) Claim in the Logout Token to identify the RP session with the OP.
+	// If supported, the sid Claim is also included in ID Tokens issued by the OP. If omitted, the default value is false.
+	BackChannelLogoutSessionSupported bool `json:"backchannel_logout_session_supported,omitempty"`
 }
 
 type AuthMethod string

pkg/oidc/token.go

@@ -382,3 +382,40 @@ type TokenExchangeResponse struct {
 	// if the requested_token_type was Access Token and scope contained openid.
 	IDToken string `json:"id_token,omitempty"`
 }
+
+type LogoutTokenClaims struct {
+	Issuer     string         `json:"iss,omitempty"`
+	Subject    string         `json:"sub,omitempty"`
+	Audience   Audience       `json:"aud,omitempty"`
+	IssuedAt   Time           `json:"iat,omitempty"`
+	Expiration Time           `json:"exp,omitempty"`
+	JWTID      string         `json:"jti,omitempty"`
+	Events     map[string]any `json:"events,omitempty"`
+	SessionID  string         `json:"sid,omitempty"`
+	Claims     map[string]any `json:"-"`
+}
+
+type ltcAlias LogoutTokenClaims
+
+func (i *LogoutTokenClaims) MarshalJSON() ([]byte, error) {
+	return mergeAndMarshalClaims((*ltcAlias)(i), i.Claims)
+}
+
+func (i *LogoutTokenClaims) UnmarshalJSON(data []byte) error {
+	return unmarshalJSONMulti(data, (*ltcAlias)(i), &i.Claims)
+}
+
+func NewLogoutTokenClaims(issuer, subject string, audience Audience, expiration time.Time, jwtID, sessionID string, skew time.Duration) *LogoutTokenClaims {
+	return &LogoutTokenClaims{
+		Issuer:     issuer,
+		Subject:    subject,
+		Audience:   audience,
+		IssuedAt:   FromTime(time.Now().Add(-skew)),
+		Expiration: FromTime(expiration),
+		JWTID:      jwtID,
+		Events: map[string]any{
+			"http://schemas.openid.net/event/backchannel-logout": struct{}{},
+		},
+		SessionID: sessionID,
+	}
+}

pkg/oidc/token_test.go

@@ -242,3 +242,39 @@ func TestIDTokenClaims_GetUserInfo(t *testing.T) {
 	got := idTokenData.GetUserInfo()
 	assert.Equal(t, want, got)
 }
+
+func TestNewLogoutTokenClaims(t *testing.T) {
+	want := &LogoutTokenClaims{
+		Issuer:     "zitadel",
+		Subject:    "hello@me.com",
+		Audience:   Audience{"foo", "just@me.com"},
+		Expiration: 12345,
+		JWTID:      "jwtID",
+		Events: map[string]any{
+			"http://schemas.openid.net/event/backchannel-logout": struct{}{},
+		},
+		SessionID: "sessionID",
+		Claims:    nil,
+	}
+
+	got := NewLogoutTokenClaims(
+		want.Issuer,
+		want.Subject,
+		want.Audience,
+		want.Expiration.AsTime(),
+		want.JWTID,
+		want.SessionID,
+		1*time.Second,
+	)
+
+	// test if the dynamic timestamp is around now,
+	// allowing for a delta of 1, just in case we flip on
+	// either side of a second boundry.
+	nowMinusSkew := NowTime() - 1
+	assert.InDelta(t, int64(nowMinusSkew), int64(got.IssuedAt), 1)
+
+	// Make equal not fail on dynamic timestamp
+	got.IssuedAt = 0
+
+	assert.Equal(t, want, got)
+}