reasonspec = "reason" [CFWS] "=" [CFWS] value
                ; a free-form comment on the reason the given result
                ; was returned

   The "value" is as defined in Section 5.1 of [MIME], with
   "quoted-string" updated as specified in [RFC6532].

var parseTests = []msgauthTest{
...
	{
		value: "example.com;" +
			"dkim=pass reason=\"good signature\" header.i=@mail-router.example.net;",
		identifier: "example.com",
		results: []Result{
			&DKIMResult{Value: ResultPass, Reason: "good signature", Identifier: "@mail-router.example.net"},
		},
	},
}