MM-22785 audit server CLI (#14144)

Add auditing to server CLI.

Also:
- simplify auditing in API layer
- reduce number of AddMeta calls
- have models serialize themselves
- more consistent field naming

audit/record.go

@@ -6,6 +6,10 @@ package audit
 // Meta represents metadata that can be added to a audit record as name/value pairs.
 type Meta map[string]interface{}
 
+// FuncMetaTypeConv defines a function that can convert meta data types into something
+// that serializes well for audit records.
+type FuncMetaTypeConv func(val interface{}) (newVal interface{}, converted bool)
+
 // Record provides a consistent set of fields used for all audit logging.
 type Record struct {
 	APIPath   string
@@ -16,6 +20,7 @@ type Record struct {
 	Client    string
 	IPAddress string
 	Meta      Meta
+	metaConv  []FuncMetaTypeConv
 }
 
 // Success marks the audit record status as successful.
@@ -33,5 +38,22 @@ func (rec *Record) AddMeta(name string, val interface{}) {
 	if rec.Meta == nil {
 		rec.Meta = Meta{}
 	}
+
+	// possibly convert val to something better suited for serializing
+	// via zero or more conversion functions.
+	var converted bool
+	for _, conv := range rec.metaConv {
+		val, converted = conv(val)
+		if converted {
+			break
+		}
+	}
+
 	rec.Meta[name] = val
 }
+
+// AddMetaTypeConverter adds a function capable of converting meta field types
+// into something more suitable for serialization.
+func (rec *Record) AddMetaTypeConverter(f FuncMetaTypeConv) {
+	rec.metaConv = append(rec.metaConv, f)
+}