How can I set the Secure flag on an ASP.NET Sessio

Question

How can I set the Secure flag on an ASP.NET Session Cookie, so that it will only be transmitted over HTTPS and never over plain HTTP?

Answer 1

There are two ways, one httpCookies element in web.config allows you to turn on requireSSL which only transmit all cookies including session in SSL only and also inside forms authentication, but if you turn on SSL on httpcookies you must also turn it on inside forms configuration too.

Edit for clarity: Put this in <system.web>

<httpCookies requireSSL="true" />

Answer 2

Things get messy quickly if you are talking about checked-in code in an enterprise environment. We've found that the best approach is to have the web.Release.config contain the following:

<system.web>
  <compilation xdt:Transform="RemoveAttributes(debug)" />
  <authentication>
      <forms xdt:Transform="Replace" timeout="20" requireSSL="true" />
  </authentication>
</system.web>

That way, developers are not affected (running in Debug), and only servers that get Release builds are requiring cookies to be SSL.

Answer 3

In the <system.web> element, add the following element:

<httpCookies requireSSL="true" />

However, if you have a <forms> element in your system.web\authentication block, then this will override the setting in httpCookies, setting it back to the default false.

In that case, you need to add the requireSSL="true" attribute to the forms element as well.

So you will end up with:

<system.web>
    <authentication mode="Forms">
        <forms requireSSL="true">
            <!-- forms content -->
        </forms>
    </authentication>
</system.web>

See here and here for MSDN documentation of these elements.