Add ability to log masked (string) values

pkg/logger/masked.go

@@ -0,0 +1,39 @@
+package logger
+
+import (
+	"fmt"
+	"strings"
+
+	"go.uber.org/zap"
+	"go.uber.org/zap/zapcore"
+)
+
+// Mask is a passthrough for MaskIf
+func Mask(key string, val interface{}) zap.Field {
+	return MaskIf(key, val, true)
+}
+
+// MaskIf conditionally masks (replaces string with * of equal length input string/stringer
+func MaskIf(key string, val interface{}, mask bool) zap.Field {
+	var str string
+
+	switch v := val.(type) {
+	case fmt.Stringer:
+		str = v.String()
+	case string:
+		str = v
+	default:
+		// empty string for other types
+		str = ""
+	}
+
+	if mask {
+		str = strings.Repeat("*", len(str))
+	}
+
+	return zap.Field{
+		Key:    key,
+		Type:   zapcore.StringType,
+		String: str,
+	}
+}