Loosen restrictions for IAM user names

The only restriction for an IAM username is that it cannot start with
a '$'. An username that contains a ':' must escape it with another ':'
for use in a token for RTMP or SRT.

encoding/token/token_test.go

@@ -0,0 +1,41 @@
+package token
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestMarshal(t *testing.T) {
+	token := "xxx"
+
+	data := [][2]string{
+		{"", ""},
+		{"foo", "foo"},
+		{"foo:bar", "foo::bar"},
+		{"foo::bar", "foo::::bar"},
+	}
+
+	for _, d := range data {
+		encoded := Marshal(d[0], token)
+		require.Equal(t, d[1]+":"+token, encoded, d[1])
+	}
+}
+
+func TestUnmarshal(t *testing.T) {
+	data := [][3]string{
+		{"foo", "", "foo"},
+		{"fo::o", "", "fo::o"},
+		{"::foo", "", "::foo"},
+		{":xxx", "", "xxx"},
+		{"foo:xxx", "foo", "xxx"},
+		{"foo::bar:xxx", "foo:bar", "xxx"},
+		{"foo::::bar:xxx", "foo::bar", "xxx"},
+	}
+
+	for _, d := range data {
+		username, token := Unmarshal(d[0])
+		require.Equal(t, d[1], username, d[0])
+		require.Equal(t, d[2], token)
+	}
+}