feat: http provider signing key addition (#10641)

# Which Problems Are Solved

HTTP Request to HTTP providers for Email or SMS are not signed.

# How the Problems Are Solved

Add a Signing Key to the HTTP Provider resources, which is then used to
generate a header to sign the payload.

# Additional Changes

Additional tests for query side of the SMTP provider.

# Additional Context

Closes #10067

---------

Co-authored-by: Marco A. <marco@zitadel.com>
(cherry picked from commit 8909b9a2a6)

internal/notification/channels/webhook/channel.go

@@ -12,6 +12,11 @@ import (
 	"github.com/zitadel/zitadel/internal/notification/channels"
 	"github.com/zitadel/zitadel/internal/notification/messages"
 	"github.com/zitadel/zitadel/internal/zerrors"
+	"github.com/zitadel/zitadel/pkg/actions"
+)
+
+const (
+	SigningHeader = "ZITADEL-Signature"
 )
 
 func InitChannel(ctx context.Context, cfg Config) (channels.NotificationChannel, error) {
@@ -39,6 +44,10 @@ func InitChannel(ctx context.Context, cfg Config) (channels.NotificationChannel,
 			req.Header = cfg.Headers
 		}
 		req.Header.Set("Content-Type", "application/json")
+		if cfg.SigningKey != "" {
+			req.Header.Set(SigningHeader, actions.ComputeSignatureHeader(time.Now(), []byte(payload), cfg.SigningKey))
+		}
+
 		resp, err := http.DefaultClient.Do(req)
 		if err != nil {
 			return err

internal/notification/channels/webhook/config.go

@@ -6,9 +6,10 @@ import (
 )
 
 type Config struct {
-	CallURL string
-	Method  string
-	Headers http.Header
+	CallURL    string
+	Method     string
+	Headers    http.Header
+	SigningKey string
 }
 
 func (w *Config) Validate() error {