from the cookies rfc6265
5. The Secure Attribute
The Secure attribute limits the scope of the cookie to "secure"
channels (where "secure" is defined by the user agent). When a
cookie has the Secure attribute, the user agent will include the
cookie in an HTTP request only if the request is transmitted over a
secure channel (typically HTTP over Transport Layer Security (TLS)
So is the user client who decides what a secure Chanel is. For browser yes, https is a secure Chanel