Session aware logout, backend logout url approach

CHANGELOG.md

@@ -22,6 +22,7 @@
 - [#2282](https://github.com/oauth2-proxy/oauth2-proxy/pull/2282) Fixed checking Google Groups membership using Google Application Credentials (@kvanzuijlen)
 - [#2183](https://github.com/oauth2-proxy/oauth2-proxy/pull/2183) Allowing relative redirect url though an option (@axel7083)
 - [#1866](https://github.com/oauth2-proxy/oauth2-proxy/pull/1866) Add support for unix socker as upstream (@babs)
+- [#1876](https://github.com/oauth2-proxy/oauth2-proxy/pull/1876) Add `--backend-logout-url` with `{id_token}` placeholder (@babs)
 - [#1949](https://github.com/oauth2-proxy/oauth2-proxy/pull/1949) Allow cookie names with dots in redis sessions (@miguelborges99)
 - [#2297](https://github.com/oauth2-proxy/oauth2-proxy/pull/2297) Add nightly build and push (@tuunit)
 - [#2329](https://github.com/oauth2-proxy/oauth2-proxy/pull/2329) Add an option to skip request to profile URL for resolving missing claims in id_token (@nilsgstrabo)

oauthproxy.go

@@ -348,15 +348,15 @@ func (p *OAuthProxy) buildProxySubrouter(s *mux.Router) {
 	s.Use(prepareNoCacheMiddleware)
 
 	s.Path(signInPath).HandlerFunc(p.SignIn)
-	s.Path(signOutPath).HandlerFunc(p.SignOut)
 	s.Path(oauthStartPath).HandlerFunc(p.OAuthStart)
 	s.Path(oauthCallbackPath).HandlerFunc(p.OAuthCallback)
 
 	// Static file paths
 	s.PathPrefix(staticPathPrefix).Handler(http.StripPrefix(p.ProxyPrefix, http.FileServer(http.FS(staticFiles))))
 
-	// The userinfo endpoint needs to load sessions before handling the request
+	// The userinfo and logout endpoints needs to load sessions before handling the request
 	s.Path(userInfoPath).Handler(p.sessionChain.ThenFunc(p.UserInfo))
+	s.Path(signOutPath).Handler(p.sessionChain.ThenFunc(p.SignOut))
 }
 
 // buildPreAuthChain constructs a chain that should process every request before
@@ -769,9 +769,43 @@ func (p *OAuthProxy) SignOut(rw http.ResponseWriter, req *http.Request) {
 		p.ErrorPage(rw, req, http.StatusInternalServerError, err.Error())
 		return
 	}
+
+	p.backendLogout(rw, req)
+
 	http.Redirect(rw, req, redirect, http.StatusFound)
 }
 
+func (p *OAuthProxy) backendLogout(rw http.ResponseWriter, req *http.Request) {
+	session, err := p.getAuthenticatedSession(rw, req)
+	if err != nil {
+		logger.Errorf("error getting authenticated session during backend logout: %v", err)
+		return
+	}
+
+	if session == nil {
+		return
+	}
+
+	providerData := p.provider.Data()
+	if providerData.BackendLogoutURL == "" {
+		return
+	}
+
+	backendLogoutURL := strings.ReplaceAll(providerData.BackendLogoutURL, "{id_token}", session.IDToken)
+	// security exception because URL is dynamic ({id_token} replacement) but
+	// base is not end-user provided but comes from configuration somewhat secure
+	resp, err := http.Get(backendLogoutURL) // #nosec G107
+	if err != nil {
+		logger.Errorf("error while calling backend logout: %v", err)
+		return
+	}
+
+	defer resp.Body.Close()
+	if resp.StatusCode != 200 {
+		logger.Errorf("error while calling backend logout url, returned error code %v", resp.StatusCode)
+	}
+}
+
 // OAuthStart starts the OAuth2 authentication flow
 func (p *OAuthProxy) OAuthStart(rw http.ResponseWriter, req *http.Request) {
 	// start the flow permitting login URL query parameters to be overridden from the request URL

pkg/apis/options/legacy_options.go

@@ -567,6 +567,7 @@ type LegacyProvider struct {
 	UserIDClaim                        string   `flag:"user-id-claim" cfg:"user_id_claim"`
 	AllowedGroups                      []string `flag:"allowed-group" cfg:"allowed_groups"`
 	AllowedRoles                       []string `flag:"allowed-role" cfg:"allowed_roles"`
+	BackendLogoutURL                   string   `flag:"backend-logout-url" cfg:"backend_logout_url"`
 
 	AcrValues  string `flag:"acr-values" cfg:"acr_values"`
 	JWTKey     string `flag:"jwt-key" cfg:"jwt_key"`
@@ -635,6 +636,7 @@ func legacyProviderFlagSet() *pflag.FlagSet {
 	flagSet.String("user-id-claim", OIDCEmailClaim, "(DEPRECATED for `oidc-email-claim`) which claim contains the user ID")
 	flagSet.StringSlice("allowed-group", []string{}, "restrict logins to members of this group (may be given multiple times)")
 	flagSet.StringSlice("allowed-role", []string{}, "(keycloak-oidc) restrict logins to members of these roles (may be given multiple times)")
+	flagSet.String("backend-logout-url", "", "url to perform a backend logout, {id_token} can be used as placeholder for the id_token")
 
 	return flagSet
 }
@@ -714,6 +716,7 @@ func (l *LegacyProvider) convert() (Providers, error) {
 		Scope:                    l.Scope,
 		AllowedGroups:            l.AllowedGroups,
 		CodeChallengeMethod:      l.CodeChallengeMethod,
+		BackendLogoutURL:         l.BackendLogoutURL,
 	}
 
 	// This part is out of the switch section for all providers that support OIDC

pkg/apis/options/providers.go

@@ -85,6 +85,8 @@ type Provider struct {
 	AllowedGroups []string `json:"allowedGroups,omitempty"`
 	// The code challenge method
 	CodeChallengeMethod string `json:"code_challenge_method,omitempty"`
+	// URL to call to perform backend logout, `{id_token}` would be replaced by the actual `id_token` if available in the session
+	BackendLogoutURL string `json:"backendLogoutURL"`
 }
 
 // ProviderType is used to enumerate the different provider type options

providers/provider_data.go

@@ -58,6 +58,8 @@ type ProviderData struct {
 	getAuthorizationHeaderFunc func(string) http.Header
 	loginURLParameterDefaults  url.Values
 	loginURLParameterOverrides map[string]*regexp.Regexp
+
+	BackendLogoutURL string
 }
 
 // Data returns the ProviderData

providers/providers.go

@@ -160,6 +160,7 @@ func newProviderDataFromConfig(providerConfig options.Provider) (*ProviderData,
 	}
 
 	p.setAllowedGroups(providerConfig.AllowedGroups)
+	p.BackendLogoutURL = providerConfig.BackendLogoutURL
 	return p, nil
 }