fix(idp): prevent server errors for idps using form post for callbacks (#9097)

# Which Problems Are Solved

Some IdP callbacks use HTTP form POST to return their data on callbacks.
For handling CSRF in the login after such calls, a 302 Found to the
corresponding non form callback (in ZITADEL) is sent. Depending on the
size of the initial form body, this could lead to ZITADEL terminating
the connection, resulting in the user not getting a response or an
intermediate proxy to return them an HTTP 502.

# How the Problems Are Solved

- the form body is parsed and stored into the ZITADEL cache (using the
configured database by default)
- the redirect (302 Found) is performed with the request id
- the callback retrieves the data from the cache instead of the query
parameters (will fallback to latter to handle open uncached requests)

# Additional Changes

- fixed a typo in the default (cache) configuration: `LastUsage` ->
`LastUseAge`

# Additional Context

- reported by a customer
- needs to be backported to current cloud version (2.66.x)

---------

Co-authored-by: Silvan <27845747+adlerhurst@users.noreply.github.com>

cmd/defaults.yaml

@@ -198,8 +198,11 @@ Caches:
       AutoPrune:
         Interval: 1m
         TimeOut: 5s
+    # Postgres connector uses the configured database (postgres or cockraochdb) as cache.
+    # It is suitable for deployments with multiple containers.
+    # The cache is enabled by default because it is the default cache states for IdP form callbacks
     Postgres:
-      Enabled: false
+      Enabled: true
       AutoPrune:
         Interval: 15m
         TimeOut: 30s
@@ -311,7 +314,7 @@ Caches:
     # When connector is empty, this cache will be disabled.
     Connector: ""
     MaxAge: 1h
-    LastUsage: 10m
+    LastUseAge: 10m
     # Log enables cache-specific logging. Default to error log to stderr when omitted.
     Log:
       Level: error
@@ -322,7 +325,7 @@ Caches:
   Milestones:
     Connector: ""
     MaxAge: 1h
-    LastUsage: 10m
+    LastUseAge: 10m
     Log:
       Level: error
       AddSource: true
@@ -332,7 +335,17 @@ Caches:
   Organization:
     Connector: ""
     MaxAge: 1h
-    LastUsage: 10m
+    LastUseAge: 10m
+    Log:
+      Level: error
+      AddSource: true
+      Formatter:
+        Format: text
+  # IdP callbacks using form POST cache, required for handling them securely and without possible too big request urls.
+  IdPFormCallbacks:
+    Connector: "postgres"
+    MaxAge: 1h
+    LastUseAge: 10m
     Log:
       Level: error
       AddSource: true

cmd/start/start.go

@@ -317,6 +317,7 @@ func startZitadel(ctx context.Context, config *Config, masterKey string, server
 		authZRepo,
 		keys,
 		permissionCheck,
+		cacheConnectors,
 	)
 	if err != nil {
 		return err
@@ -361,6 +362,7 @@ func startAPIs(
 	authZRepo authz_repo.Repository,
 	keys *encryption.EncryptionKeys,
 	permissionCheck domain.PermissionCheck,
+	cacheConnectors connector.Connectors,
 ) (*api.API, error) {
 	repo := struct {
 		authz_repo.Repository
@@ -542,6 +544,7 @@ func startAPIs(
 		keys.User,
 		keys.IDPConfig,
 		keys.CSRFCookieKey,
+		cacheConnectors,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("unable to start login: %w", err)

internal/api/ui/login/external_provider_handler.go

@@ -214,8 +214,20 @@ func (l *Login) handleExternalLoginCallbackForm(w http.ResponseWriter, r *http.R
 		l.renderLogin(w, r, nil, err)
 		return
 	}
-	r.Form.Add("Method", http.MethodPost)
-	http.Redirect(w, r, HandlerPrefix+EndpointExternalLoginCallback+"?"+r.Form.Encode(), 302)
+	state := r.Form.Get("state")
+	if state == "" {
+		state = r.Form.Get("RelayState")
+	}
+	if state == "" {
+		l.renderLogin(w, r, nil, zerrors.ThrowInvalidArgument(nil, "LOGIN-dsg3f", "Errors.AuthRequest.NotFound"))
+		return
+	}
+	l.caches.idpFormCallbacks.Set(r.Context(), &idpFormCallback{
+		InstanceID: authz.GetInstance(r.Context()).InstanceID(),
+		State:      state,
+		Form:       r.Form,
+	})
+	http.Redirect(w, r, HandlerPrefix+EndpointExternalLoginCallback+"?method=POST&state="+state, 302)
 }
 
 // handleExternalLoginCallback handles the callback from a IDP
@@ -232,8 +244,7 @@ func (l *Login) handleExternalLoginCallback(w http.ResponseWriter, r *http.Reque
 	}
 	// workaround because of CSRF on external identity provider flows
 	if data.Method == http.MethodPost {
-		r.Method = http.MethodPost
-		r.PostForm = r.Form
+		l.setDataFromFormCallback(r, data.State)
 	}
 
 	userAgentID, _ := http_mw.UserAgentIDFromCtx(r.Context())
@@ -345,6 +356,17 @@ func (l *Login) handleExternalLoginCallback(w http.ResponseWriter, r *http.Reque
 	l.handleExternalUserAuthenticated(w, r, authReq, identityProvider, session, user, l.renderNextStep)
 }
 
+func (l *Login) setDataFromFormCallback(r *http.Request, state string) {
+	r.Method = http.MethodPost
+	// fallback to the form data in case the request was started before the cache was implemented
+	r.PostForm = r.Form
+	idpCallback, ok := l.caches.idpFormCallbacks.Get(r.Context(), idpFormCallbackIndexRequestID,
+		idpFormCallbackKey(authz.GetInstance(r.Context()).InstanceID(), state))
+	if ok {
+		r.PostForm = idpCallback.Form
+	}
+}
+
 func (l *Login) tryMigrateExternalUserID(r *http.Request, session idp.Session, authReq *domain.AuthRequest, externalUser *domain.ExternalUser) (previousIDMatched bool, err error) {
 	migration, ok := session.(idp.SessionSupportsMigration)
 	if !ok {

internal/api/ui/login/login.go

@@ -3,6 +3,7 @@ package login
 import (
 	"context"
 	"net/http"
+	"net/url"
 	"strings"
 	"time"
 
@@ -15,6 +16,8 @@ import (
 	_ "github.com/zitadel/zitadel/internal/api/ui/login/statik"
 	auth_repository "github.com/zitadel/zitadel/internal/auth/repository"
 	"github.com/zitadel/zitadel/internal/auth/repository/eventsourcing"
+	"github.com/zitadel/zitadel/internal/cache"
+	"github.com/zitadel/zitadel/internal/cache/connector"
 	"github.com/zitadel/zitadel/internal/command"
 	"github.com/zitadel/zitadel/internal/crypto"
 	"github.com/zitadel/zitadel/internal/domain"
@@ -38,6 +41,7 @@ type Login struct {
 	samlAuthCallbackURL func(context.Context, string) string
 	idpConfigAlg        crypto.EncryptionAlgorithm
 	userCodeAlg         crypto.EncryptionAlgorithm
+	caches              *Caches
 }
 
 type Config struct {
@@ -74,6 +78,7 @@ func CreateLogin(config Config,
 	userCodeAlg crypto.EncryptionAlgorithm,
 	idpConfigAlg crypto.EncryptionAlgorithm,
 	csrfCookieKey []byte,
+	cacheConnectors connector.Connectors,
 ) (*Login, error) {
 	login := &Login{
 		oidcAuthCallbackURL: oidcAuthCallbackURL,
@@ -94,6 +99,12 @@ func CreateLogin(config Config,
 	login.router = CreateRouter(login, middleware.TelemetryHandler(IgnoreInstanceEndpoints...), oidcInstanceHandler, samlInstanceHandler, csrfInterceptor, cacheInterceptor, security, userAgentCookie, issuerInterceptor, accessHandler)
 	login.renderer = CreateRenderer(HandlerPrefix, staticStorage, config.LanguageCookieName)
 	login.parser = form.NewParser()
+
+	var err error
+	login.caches, err = startCaches(context.Background(), cacheConnectors)
+	if err != nil {
+		return nil, err
+	}
 	return login, nil
 }
 
@@ -201,3 +212,41 @@ func setUserContext(ctx context.Context, userID, resourceOwner string) context.C
 func (l *Login) baseURL(ctx context.Context) string {
 	return http_utils.DomainContext(ctx).Origin() + HandlerPrefix
 }
+
+type Caches struct {
+	idpFormCallbacks cache.Cache[idpFormCallbackIndex, string, *idpFormCallback]
+}
+
+func startCaches(background context.Context, connectors connector.Connectors) (_ *Caches, err error) {
+	caches := new(Caches)
+	caches.idpFormCallbacks, err = connector.StartCache[idpFormCallbackIndex, string, *idpFormCallback](background, []idpFormCallbackIndex{idpFormCallbackIndexRequestID}, cache.PurposeIdPFormCallback, connectors.Config.IdPFormCallbacks, connectors)
+	if err != nil {
+		return nil, err
+	}
+	return caches, nil
+}
+
+type idpFormCallbackIndex int
+
+const (
+	idpFormCallbackIndexUnspecified idpFormCallbackIndex = iota
+	idpFormCallbackIndexRequestID
+)
+
+type idpFormCallback struct {
+	InstanceID string
+	State      string
+	Form       url.Values
+}
+
+// Keys implements cache.Entry
+func (c *idpFormCallback) Keys(i idpFormCallbackIndex) []string {
+	if i == idpFormCallbackIndexRequestID {
+		return []string{idpFormCallbackKey(c.InstanceID, c.State)}
+	}
+	return nil
+}
+
+func idpFormCallbackKey(instanceID, state string) string {
+	return instanceID + "-" + state
+}

internal/cache/cache.go

@@ -17,6 +17,7 @@ const (
 	PurposeAuthzInstance
 	PurposeMilestones
 	PurposeOrganization
+	PurposeIdPFormCallback
 )
 
 // Cache stores objects with a value of type `V`.

internal/cache/connector/connector.go

@@ -19,9 +19,10 @@ type CachesConfig struct {
 		Postgres pg.Config
 		Redis    redis.Config
 	}
-	Instance     *cache.Config
-	Milestones   *cache.Config
-	Organization *cache.Config
+	Instance         *cache.Config
+	Milestones       *cache.Config
+	Organization     *cache.Config
+	IdPFormCallbacks *cache.Config
 }
 
 type Connectors struct {

internal/cache/purpose_enumer.go

@@ -7,11 +7,11 @@ import (
 	"strings"
 )
 
-const _PurposeName = "unspecifiedauthz_instancemilestonesorganization"
+const _PurposeName = "unspecifiedauthz_instancemilestonesorganizationid_p_form_callback"
 
-var _PurposeIndex = [...]uint8{0, 11, 25, 35, 47}
+var _PurposeIndex = [...]uint8{0, 11, 25, 35, 47, 65}
 
-const _PurposeLowerName = "unspecifiedauthz_instancemilestonesorganization"
+const _PurposeLowerName = "unspecifiedauthz_instancemilestonesorganizationid_p_form_callback"
 
 func (i Purpose) String() string {
 	if i < 0 || i >= Purpose(len(_PurposeIndex)-1) {
@@ -28,9 +28,10 @@ func _PurposeNoOp() {
 	_ = x[PurposeAuthzInstance-(1)]
 	_ = x[PurposeMilestones-(2)]
 	_ = x[PurposeOrganization-(3)]
+	_ = x[PurposeIdPFormCallback-(4)]
 }
 
-var _PurposeValues = []Purpose{PurposeUnspecified, PurposeAuthzInstance, PurposeMilestones, PurposeOrganization}
+var _PurposeValues = []Purpose{PurposeUnspecified, PurposeAuthzInstance, PurposeMilestones, PurposeOrganization, PurposeIdPFormCallback}
 
 var _PurposeNameToValueMap = map[string]Purpose{
 	_PurposeName[0:11]:       PurposeUnspecified,
@@ -41,6 +42,8 @@ var _PurposeNameToValueMap = map[string]Purpose{
 	_PurposeLowerName[25:35]: PurposeMilestones,
 	_PurposeName[35:47]:      PurposeOrganization,
 	_PurposeLowerName[35:47]: PurposeOrganization,
+	_PurposeName[47:65]:      PurposeIdPFormCallback,
+	_PurposeLowerName[47:65]: PurposeIdPFormCallback,
 }
 
 var _PurposeNames = []string{
@@ -48,6 +51,7 @@ var _PurposeNames = []string{
 	_PurposeName[11:25],
 	_PurposeName[25:35],
 	_PurposeName[35:47],
+	_PurposeName[47:65],
 }
 
 // PurposeString retrieves an enum value from the enum constants string name.