feat(OIDC): add back channel logout (#8837)

# Which Problems Are Solved

Currently ZITADEL supports RP-initiated logout for clients. Back-channel
logout ensures that user sessions are terminated across all connected
applications, even if the user closes their browser or loses
connectivity providing a more secure alternative for certain use cases.

# How the Problems Are Solved

If the feature is activated and the client used for the authentication
has a back_channel_logout_uri configured, a
`session_logout.back_channel` will be registered. Once a user terminates
their session, a (notification) handler will send a SET (form POST) to
the registered uri containing a logout_token (with the user's ID and
session ID).

- A new feature "back_channel_logout" is added on system and instance
level
- A `back_channel_logout_uri` can be managed on OIDC applications
- Added a `session_logout` aggregate to register and inform about sent
`back_channel` notifications
- Added a `SecurityEventToken` channel and `Form`message type in the
notification handlers
- Added `TriggeredAtOrigin` fields to `HumanSignedOut` and
`TerminateSession` events for notification handling
- Exported various functions and types in the `oidc` package to be able
to reuse for token signing in the back_channel notifier.
- To prevent that current existing session termination events will be
handled, a setup step is added to set the `current_states` for the
`projections.notifications_back_channel_logout` to the current position

- [x] requires https://github.com/zitadel/oidc/pull/671

# Additional Changes

- Updated all OTEL dependencies to v1.29.0, since OIDC already updated
some of them to that version.
- Single Session Termination feature is correctly checked (fixed feature
mapping)

# Additional Context

- closes https://github.com/zitadel/zitadel/issues/8467
- TODO:
  - Documentation
  - UI to be done: https://github.com/zitadel/zitadel/issues/8469

---------

Co-authored-by: Hidde Wieringa <hidde@hiddewieringa.nl>

internal/repository/project/oidc_config.go

@@ -43,6 +43,7 @@ type OIDCConfigAddedEvent struct {
 	ClockSkew                time.Duration              `json:"clockSkew,omitempty"`
 	AdditionalOrigins        []string                   `json:"additionalOrigins,omitempty"`
 	SkipNativeAppSuccessPage bool                       `json:"skipNativeAppSuccessPage,omitempty"`
+	BackChannelLogoutURI     string                     `json:"backChannelLogoutURI,omitempty"`
 }
 
 func (e *OIDCConfigAddedEvent) Payload() interface{} {
@@ -74,6 +75,7 @@ func NewOIDCConfigAddedEvent(
 	clockSkew time.Duration,
 	additionalOrigins []string,
 	skipNativeAppSuccessPage bool,
+	backChannelLogoutURI string,
 ) *OIDCConfigAddedEvent {
 	return &OIDCConfigAddedEvent{
 		BaseEvent: *eventstore.NewBaseEventForPush(
@@ -99,6 +101,7 @@ func NewOIDCConfigAddedEvent(
 		ClockSkew:                clockSkew,
 		AdditionalOrigins:        additionalOrigins,
 		SkipNativeAppSuccessPage: skipNativeAppSuccessPage,
+		BackChannelLogoutURI:     backChannelLogoutURI,
 	}
 }
 
@@ -184,7 +187,10 @@ func (e *OIDCConfigAddedEvent) Validate(cmd eventstore.Command) bool {
 			return false
 		}
 	}
-	return e.SkipNativeAppSuccessPage == c.SkipNativeAppSuccessPage
+	if e.SkipNativeAppSuccessPage != c.SkipNativeAppSuccessPage {
+		return false
+	}
+	return e.BackChannelLogoutURI == c.BackChannelLogoutURI
 }
 
 func OIDCConfigAddedEventMapper(event eventstore.Event) (eventstore.Event, error) {
@@ -219,6 +225,7 @@ type OIDCConfigChangedEvent struct {
 	ClockSkew                *time.Duration              `json:"clockSkew,omitempty"`
 	AdditionalOrigins        *[]string                   `json:"additionalOrigins,omitempty"`
 	SkipNativeAppSuccessPage *bool                       `json:"skipNativeAppSuccessPage,omitempty"`
+	BackChannelLogoutURI     *string                     `json:"backChannelLogoutURI,omitempty"`
 }
 
 func (e *OIDCConfigChangedEvent) Payload() interface{} {
@@ -345,6 +352,12 @@ func ChangeSkipNativeAppSuccessPage(skipNativeAppSuccessPage bool) func(event *O
 	}
 }
 
+func ChangeBackChannelLogoutURI(backChannelLogoutURI string) func(event *OIDCConfigChangedEvent) {
+	return func(e *OIDCConfigChangedEvent) {
+		e.BackChannelLogoutURI = &backChannelLogoutURI
+	}
+}
+
 func OIDCConfigChangedEventMapper(event eventstore.Event) (eventstore.Event, error) {
 	e := &OIDCConfigChangedEvent{
 		BaseEvent: *eventstore.BaseEventFromRepo(event),