WSO2 Identity Server - How to assign an existing role to a WSO2 IS user?

Question

I am using WSO2 Identity Server 4.1.0. My requirement is to assign an existing role to a user created in the WSO2 default identity store. I have tried the following:

Answer 1

Use PATCH operation:

Nodejs Sample code for SCIM2 (WSO2 Identity server 5.6):

//roleId is GUID generated after creating group. 
// token is the bearer token generated via client credential or password credential

function assignRoleToUser(token, user, roleId) {
var groupId = roleId;
var rp = require('request-promise');
var options = {
    uri:  + '/' + groupId,
    method: 'PATCH',
    json: true,
    headers: {
        'Content-Type': 'application/json',
        'Authorization': token
    },
    body:
    {
        schemas: ['urn:ietf:params:scim:api:messages:2.0:PatchOp'],
        Operations: [
            {
                op: 'add',
                value: {
                    members: [
                        {
                            display: user.userName,
                            value: user.id
                        }
                    ]

                }
            }]
    }
};
return rp(options);

}

Only drawback of this API is that, it returns array containing all members of that group after success. Not optimized if group has thousands or millions of users.