Add log redacting, controlled by the new EnableLogRedacting config option (default true)

Imported redacting code from https://github.com/whuang8/redactrus (thanks William Huang)
Didn't use it as a dependency as it was too small and we want to keep dependencies at a minimum

log/redactrus.go

@@ -0,0 +1,70 @@
+package log
+
+// Copied from https://github.com/whuang8/redactrus (MIT License)
+// Copyright (c) 2018 William Huang
+
+import (
+	"reflect"
+	"regexp"
+
+	"github.com/sirupsen/logrus"
+)
+
+// Hook is a logrus hook for redacting information from logs
+type Hook struct {
+	// Messages with a log level not contained in this array
+	// will not be dispatched. If empty, all messages will be dispatched.
+	AcceptedLevels []logrus.Level
+	RedactionList  []string
+}
+
+// Levels returns the user defined AcceptedLevels
+// If AcceptedLevels is empty, all logrus levels are returned
+func (h *Hook) Levels() []logrus.Level {
+	if len(h.AcceptedLevels) == 0 {
+		return logrus.AllLevels
+	}
+	return h.AcceptedLevels
+}
+
+// LevelThreshold returns a []logrus.Level including all levels
+// above and including the level given. If the provided level does not exit,
+// an empty slice is returned.
+func LevelThreshold(l logrus.Level) []logrus.Level {
+	//nolint
+	if l < 0 || int(l) > len(logrus.AllLevels) {
+		return []logrus.Level{}
+	}
+	return logrus.AllLevels[:l+1]
+}
+
+// Fire redacts values in an log Entry that match
+// with keys defined in the RedactionList
+func (h *Hook) Fire(e *logrus.Entry) error {
+	for _, redactionKey := range h.RedactionList {
+		re, err := regexp.Compile(redactionKey)
+		if err != nil {
+			return err
+		}
+
+		// Redact based on key matching in Data fields
+		for k, v := range e.Data {
+			if re.MatchString(k) {
+				e.Data[k] = "[REDACTED]"
+				continue
+			}
+
+			// Redact based on value matching in Data fields
+			switch reflect.TypeOf(v).Kind() {
+			case reflect.String:
+				e.Data[k] = re.ReplaceAllString(v.(string), "$1[REDACTED]$2")
+				continue
+			}
+		}
+
+		// Redact based on text matching in the Message field
+		e.Message = re.ReplaceAllString(e.Message, "$1[REDACTED]$2")
+	}
+
+	return nil
+}