feat: Hide secrets on api and channels

server/internal/models/channel.go

@@ -14,6 +14,28 @@ const (
 	ChannelTelegram = "telegram"
 )
 
+// RedactedSecret is what a channel's secret config values read as over the API.
+// It is a sentinel and not merely a mask: a client may write it straight back,
+// and the value it stood for is preserved. See NotificationChannel.Redacted.
+const RedactedSecret = "••••••••"
+
+// channelSecretKeys names, per channel type, the config entries that are
+// credentials rather than settings. A Slack or Discord webhook URL is on this
+// list because possession of the URL *is* the authorisation to post to that
+// channel — there is nothing else to steal.
+var channelSecretKeys = map[string][]string{
+	ChannelWebhook:  {"url"},
+	ChannelSlack:    {"url"},
+	ChannelDiscord:  {"url"},
+	ChannelTelegram: {"token"},
+	ChannelSMTP:     {"password"},
+}
+
+// ChannelSecretKeys reports which config keys of a channel type are secret.
+func ChannelSecretKeys(channelType string) []string {
+	return channelSecretKeys[channelType]
+}
+
 type NotificationChannel struct {
 	ID         bson.ObjectID     `bson:"_id,omitempty" json:"_id,omitempty"`
 	InstanceID string            `bson:"instance_id" json:"instance_id"`
@@ -24,3 +46,25 @@ type NotificationChannel struct {
 	Enabled    bool              `bson:"enabled" json:"enabled"`
 	CreatedAt  time.Time         `bson:"created_at" json:"created_at"`
 }
+
+// Redacted returns a copy with every secret config value replaced by
+// RedactedSecret, for handing to a client. Nothing internal uses it: the
+// dispatchers read the stored document through GetChannel/GetChannels, so the
+// redaction is a property of the API boundary and cannot break delivery.
+//
+// A set-but-secret key keeps its key, so a caller can still tell configured
+// from absent; an empty value is left empty rather than being dressed up as a
+// credential that is not there.
+func (c NotificationChannel) Redacted() NotificationChannel {
+	out := c
+	out.Config = make(map[string]string, len(c.Config))
+	for k, v := range c.Config {
+		out.Config[k] = v
+	}
+	for _, k := range ChannelSecretKeys(c.Type) {
+		if out.Config[k] != "" {
+			out.Config[k] = RedactedSecret
+		}
+	}
+	return out
+}