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>

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.