providers/proxy: improve SLO by backchannel logging out sessions (#7099)

* outposts: add support for provider-specific websocket messages

Signed-off-by: Jens Langhammer <jens@goauthentik.io>

* providers/proxy: add custom signal on logout to logout in provider

Signed-off-by: Jens Langhammer <jens@goauthentik.io>

---------

Signed-off-by: Jens Langhammer <jens@goauthentik.io>

internal/outpost/proxyv2/application/claims.go

@@ -11,10 +11,11 @@ type Claims struct {
 	Exp               int          `json:"exp"`
 	Email             string       `json:"email"`
 	Verified          bool         `json:"email_verified"`
-	Proxy             *ProxyClaims `json:"ak_proxy"`
 	Name              string       `json:"name"`
 	PreferredUsername string       `json:"preferred_username"`
 	Groups            []string     `json:"groups"`
+	Sid               string       `json:"sid"`
+	Proxy             *ProxyClaims `json:"ak_proxy"`
 
 	RawToken string
 }