Is it not possible to add user to SharePoint group using REST for cross domain calls?

Question

I am trying to add user to a SharePoint group in a "SharePoint Hosted App". First I am checking whether the user exists in that particular group or not. If not, I am trying to add that user to a group. But it is giving me the error as

A potentially dangerous Request.Path value was detected from the client (:).

What could be the issue? I am using REST query in SharePoint Online (Office 365). Here is my code:

function AddUserToGroup(groupid,userEmail,siteurl,userKey,userId) {
    executor = new SP.RequestExecutor(appweburl);
        executor.executeAsync({
            url: appweburl + appweburl+"/_api/SP.AppContextSite(@target)/web/sitegroups("+groupid+")/users?@target='"+siteurl+"'",
            method: "POST",
            headers: { Accept: "application/json;odata=verbose", "content-type": "application/json;odata=verbose" },
            body: "{ '__metadata': { 'type': 'SP.User' }, 'LoginName': 'i:0#.f|membership|"+userEmail+"' }",
            success: AddUser_Success,
            error: AddUser_Failure
        });
    }

I followed the example which was demonstrated in the MSDN site.

Answer 1

Remove the extra "appweburl" on line 4. Your URL will look like "http://servername.comhttp://servername.com/api...." doing it the way you have posted.