Add Cookies.Delete method

cookies.go

@@ -44,3 +44,16 @@ func (c *Cookies) SetWithExpirationTime(name, value string, expires time.Time) {
 
 	http.SetCookie(c.res, &ck)
 }
+
+// Delete sets a header that tells the browser to remove the cookie with the given name.
+func (c *Cookies) Delete(name string) {
+	ck := http.Cookie{
+		Name:  name,
+		Value: "v",
+		// Setting a time in the distant past, like the unix epoch, removes the cookie,
+		// since it has long expired.
+		Expires: time.Unix(0, 0),
+	}
+
+	http.SetCookie(c.res, &ck)
+}

cookies_test.go

@@ -51,3 +51,15 @@ func TestCookies_SetWithExpirationTime(t *testing.T) {
 	h := res.Header().Get("Set-Cookie")
 	r.Equal("name=Rob Pike; Expires=Sat, 29 Jul 2017 19:28:45 GMT", h)
 }
+
+func TestCookies_Delete(t *testing.T) {
+	r := require.New(t)
+	res := httptest.NewRecorder()
+
+	c := Cookies{&http.Request{}, res}
+
+	c.Delete("remove-me")
+
+	h := res.Header().Get("Set-Cookie")
+	r.Equal("remove-me=v; Expires=Thu, 01 Jan 1970 00:00:00 GMT", h)
+}