Assigning permission to SharePoint 2013 group using REST API

Question

Hi All,
I was trying to assign permission to a group using REST but it failing with error message "Bad Request". Below is my REST code to assign Contribute permission to group with ID 95, It would great help if someone can help me to fix this.
// Set permission on a specific group
$.ajax({
url: "<Site URL>/_api/web/roleassignments/addroleassignment(principalid=95, roledefid=1073741827)",
type: "POST",
contentType: "application/json;odata=verbose",
headers: { "Accept": "application/json; odata=verbose","X-RequestDigest": $("#__REQUESTDIGEST").val(),"X-HTTP-Method": "POST" },
success: function (data) {
// Returning the results
alert('Contribute permission set on group');
alert("Error: " + JSON.stringify(data));
error: function (data) {
alert("Error: " + JSON.stringify(data));
~Harish

Answer 1

Hi Harish,
I have same problem and I just find solution for this error.
You must set body/data to null value --> It's work for me  !!! :)
See my code with RequestExecutor (I develop an SharePoint App)
// Set the new role assignment for the group on the list.
        this.setNewRoleForGroup = function (listTitle, newRoleDefId, groupId) {
            var deferred = $.Deferred();
            //First we must call the EnsureSetup method
            JSRequest.EnsureSetup();
            var hostweburl = decodeURIComponent(JSRequest.QueryString["SPHostUrl"]);
            var appweburl = decodeURIComponent(JSRequest.QueryString["SPAppWebUrl"]);
            //Tip to have a title formated to REST call
            var arrayTitle = decodeURIComponent(listTitle).split("'");
            var restQueryUrl = appweburl + "/_api/SP.AppContextSite(@target)/web/lists/GetByTitle('" + arrayTitle.join("''") + "')/roleassignments/addroleassignment(principalid=" + groupId + ",roledefid=" + newRoleDefId + ")?@target='" + hostweburl + "'";
            var executor = new SP.RequestExecutor(appweburl);
            executor.executeAsync({
                url: restQueryUrl,
                body: null,
                method: "POST",
                headers: {
                    "Content-Type": "application/json;odata=verbose",
                    "Accept": "application/json; odata=verbose",
                    "X-HTTP-Method": "POST"
                success: function (data, textStatus, xhr) {
                    deferred.resolve({ updated: true });
                error: function (xhr, textStatus, errorThrown) {
                    deferred.reject(JSON.parse(xhr.body).error.message.value);
            return deferred;