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

README.md

@@ -102,19 +102,20 @@ Here is json equivalent for one of the default users
 
 ## Features
 
-|                      | Relying party | OpenID Provider | Specification                             |
-| -------------------- | ------------- | --------------- | ----------------------------------------- |
-| Code Flow            | yes           | yes             | OpenID Connect Core 1.0, [Section 3.1][1] |
-| Implicit Flow        | no[^1]        | yes             | OpenID Connect Core 1.0, [Section 3.2][2] |
-| Hybrid Flow          | no            | not yet         | OpenID Connect Core 1.0, [Section 3.3][3] |
-| Client Credentials   | yes           | yes             | OpenID Connect Core 1.0, [Section 9][4]   |
-| Refresh Token        | yes           | yes             | OpenID Connect Core 1.0, [Section 12][5]  |
-| Discovery            | yes           | yes             | OpenID Connect [Discovery][6] 1.0         |
-| JWT Profile          | yes           | yes             | [RFC 7523][7]                             |
-| PKCE                 | yes           | yes             | [RFC 7636][8]                             |
-| Token Exchange       | yes           | yes             | [RFC 8693][9]                             |
-| Device Authorization | yes           | yes             | [RFC 8628][10]                            |
-| mTLS                 | not yet       | not yet         | [RFC 8705][11]                            |
+|                      | Relying party | OpenID Provider | Specification                                |
+|----------------------| ------------- | --------------- |----------------------------------------------|
+| Code Flow            | yes           | yes             | OpenID Connect Core 1.0, [Section 3.1][1]    |
+| Implicit Flow        | no[^1]        | yes             | OpenID Connect Core 1.0, [Section 3.2][2]    |
+| Hybrid Flow          | no            | not yet         | OpenID Connect Core 1.0, [Section 3.3][3]    |
+| Client Credentials   | yes           | yes             | OpenID Connect Core 1.0, [Section 9][4]      |
+| Refresh Token        | yes           | yes             | OpenID Connect Core 1.0, [Section 12][5]     |
+| Discovery            | yes           | yes             | OpenID Connect [Discovery][6] 1.0            |
+| JWT Profile          | yes           | yes             | [RFC 7523][7]                                |
+| PKCE                 | yes           | yes             | [RFC 7636][8]                                |
+| Token Exchange       | yes           | yes             | [RFC 8693][9]                                |
+| Device Authorization | yes           | yes             | [RFC 8628][10]                               |
+| mTLS                 | not yet       | not yet         | [RFC 8705][11]                               |
+| Back-Channel Logout  | not yet       | yes             | OpenID Connect [Back-Channel Logout][12] 1.0 |
 
 [1]: <https://openid.net/specs/openid-connect-core-1_0.html#CodeFlowAuth> "3.1. Authentication using the Authorization Code Flow"
 [2]: <https://openid.net/specs/openid-connect-core-1_0.html#ImplicitFlowAuth> "3.2. Authentication using the Implicit Flow"
@@ -127,6 +128,7 @@ Here is json equivalent for one of the default users
 [9]: <https://www.rfc-editor.org/rfc/rfc8693.html> "OAuth 2.0 Token Exchange"
 [10]: <https://www.rfc-editor.org/rfc/rfc8628.html> "OAuth 2.0 Device Authorization Grant"
 [11]: <https://www.rfc-editor.org/rfc/rfc8705.html> "OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access Tokens"
+[12]: <https://openid.net/specs/openid-connect-backchannel-1_0.html> "OpenID Connect Back-Channel Logout 1.0 incorporating errata set 1"
 
 ## Contributors
 

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:    "[email protected]",
+		Audience:   Audience{"foo", "[email protected]"},
+		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)
+}

pkg/op/config.go

@@ -49,6 +49,9 @@ type Configuration interface {
 
 	SupportedUILocales() []language.Tag
 	DeviceAuthorization() DeviceAuthorizationConfig
+
+	BackChannelLogoutSupported() bool
+	BackChannelLogoutSessionSupported() bool
 }
 
 type IssuerFromRequest func(r *http.Request) string

pkg/op/discovery.go

@@ -61,6 +61,8 @@ func CreateDiscoveryConfig(ctx context.Context, config Configuration, storage Di
 		CodeChallengeMethodsSupported:                      CodeChallengeMethods(config),
 		UILocalesSupported:                                 config.SupportedUILocales(),
 		RequestParameterSupported:                          config.RequestObjectSupported(),
+		BackChannelLogoutSupported:                         config.BackChannelLogoutSupported(),
+		BackChannelLogoutSessionSupported:                  config.BackChannelLogoutSessionSupported(),
 	}
 }
 
@@ -92,6 +94,8 @@ func createDiscoveryConfigV2(ctx context.Context, config Configuration, storage
 		CodeChallengeMethodsSupported:                      CodeChallengeMethods(config),
 		UILocalesSupported:                                 config.SupportedUILocales(),
 		RequestParameterSupported:                          config.RequestObjectSupported(),
+		BackChannelLogoutSupported:                         config.BackChannelLogoutSupported(),
+		BackChannelLogoutSessionSupported:                  config.BackChannelLogoutSessionSupported(),
 	}
 }
 

pkg/op/op.go

@@ -158,16 +158,18 @@ func authCallbackPath(o OpenIDProvider) string {
 }
 
 type Config struct {
-	CryptoKey                [32]byte
-	DefaultLogoutRedirectURI string
-	CodeMethodS256           bool
-	AuthMethodPost           bool
-	AuthMethodPrivateKeyJWT  bool
-	GrantTypeRefreshToken    bool
-	RequestObjectSupported   bool
-	SupportedUILocales       []language.Tag
-	SupportedClaims          []string
-	DeviceAuthorization      DeviceAuthorizationConfig
+	CryptoKey                         [32]byte
+	DefaultLogoutRedirectURI          string
+	CodeMethodS256                    bool
+	AuthMethodPost                    bool
+	AuthMethodPrivateKeyJWT           bool
+	GrantTypeRefreshToken             bool
+	RequestObjectSupported            bool
+	SupportedUILocales                []language.Tag
+	SupportedClaims                   []string
+	DeviceAuthorization               DeviceAuthorizationConfig
+	BackChannelLogoutSupported        bool
+	BackChannelLogoutSessionSupported bool
 }
 
 // Endpoints defines endpoint routes.
@@ -411,6 +413,14 @@ func (o *Provider) DeviceAuthorization() DeviceAuthorizationConfig {
 	return o.config.DeviceAuthorization
 }
 
+func (o *Provider) BackChannelLogoutSupported() bool {
+	return o.config.BackChannelLogoutSupported
+}
+
+func (o *Provider) BackChannelLogoutSessionSupported() bool {
+	return o.config.BackChannelLogoutSessionSupported
+}
+
 func (o *Provider) Storage() Storage {
 	return o.storage
 }