fix: recover from request panics (#11713)

# Which Problems Are Solved

Panics may cause a service discruption by unexpectedly closing an
request's connection. Or in the case of gRPC completely killing the
service.

Allthough panics are still individual bugs that need to be solved, this
PR makes sure a panic is gracefully handled and an understandable error
is returned to the client.

# How the Problems Are Solved

- Recover in the middleware interceptors for the 3 API protocols (HTTP,
gRPC, connect).
- HTTP middleware uses formatted responses for:
  - OIDC errors (JSON formatted response)
  - UI (error page rendering)
  - SCIM
- Upon recovery an alert level log is printed (ERROR+4 for stdlib log
handlers)

# Additional Context

- internal observation

---------

Co-authored-by: Livio Spring <[email protected]>
Co-authored-by: Livio Spring <[email protected]>

internal/api/grpc/server/middleware/error_interceptor.go

@@ -2,11 +2,13 @@ package middleware
 
 import (
 	"context"
+	"fmt"
 
 	"google.golang.org/grpc"
 
 	"github.com/zitadel/zitadel/internal/api/grpc/gerrors"
 	_ "github.com/zitadel/zitadel/internal/statik"
+	"github.com/zitadel/zitadel/internal/zerrors"
 )
 
 func ErrorHandler() grpc.UnaryServerInterceptor {
@@ -15,7 +17,21 @@ func ErrorHandler() grpc.UnaryServerInterceptor {
 	}
 }
 
-func toGRPCError(ctx context.Context, req interface{}, handler grpc.UnaryHandler) (interface{}, error) {
-	resp, err := handler(ctx, req)
-	return resp, gerrors.ZITADELToGRPCError(ctx, err)
+func toGRPCError(ctx context.Context, req interface{}, handler grpc.UnaryHandler) (_ interface{}, err error) {
+	ctx, cancel := context.WithCancelCause(ctx)
+	defer func() {
+		if rec := recover(); rec != nil {
+			recErr, ok := rec.(error)
+			if !ok {
+				recErr = fmt.Errorf("%v", rec)
+			}
+			if recErr != nil {
+				err = zerrors.ThrowInternal(recErr, zerrors.IDRecover, "Errors.Internal")
+			}
+		}
+		cause := err // avoid passing the transport error as cancel cause.
+		err = gerrors.ZITADELToGRPCError(ctx, err)
+		cancel(cause)
+	}()
+	return handler(ctx, req)
 }