Enum iron::headers::AccessControlAllowOrigin  
            [-] [+]
        [src]
pub enum AccessControlAllowOrigin {
    Any,
    Null,
    Value(Url),
}The Access-Control-Allow-Origin response header,
part of CORS
The Access-Control-Allow-Origin header indicates whether a resource
can be shared based by returning the value of the Origin request header,
"*", or "null" in the response.
ABNF
Access-Control-Allow-Origin = "Access-Control-Allow-Origin" ":" origin-list-or-null | "*"
Example values
null*http://google.com/
Variants
Any | Allow all origins  | 
Null | A hidden origin  | 
Value | Allow one particular origin  |