<rewrite>
    <rules>
        <rule name="GetEnvironmentInfo">
            <match url=".*" />
            <serverVariables>
                <set name="Environment" value="Dev" />
            </serverVariables>
            <action type="Rewrite" url="{R:0}" />
        </rule>
    </rules>
</rewrite>

string output = string.Empty;
if (Request.Properties.ContainsKey("MS_HttpContext"))
{
    output = ((System.Web.HttpContextWrapper)Request.Properties["MS_HttpContext"]).Request.ServerVariables["Environment"];
}
else if (Request.Properties.ContainsKey("MS_OwinContext"))
{
    var httpContextWrapper = ((OwinContext)Request.Properties["MS_OwinContext"]).Environment["System.Web.HttpContextBase"] as HttpContextWrapper;
    output = httpContextWrapper.Request.ServerVariables["Environment"];
}