create principle / httpcontextbase.User from users ID - asp.net

Question

I am using cors and asp.net membership to manage security for an API. However in some cases, the server may need to speak to our api, on behalf of the client. As in UI mvc project code behind > API.
Because the server, not authorised client would be making this call, the asp.net cookie would not be woking or picked up.
I have overloaded AuthorizeCore in order to check to see if there is a token:
if(httpContext.Request.Headers["x-access-token"] != null)
{
// this authorization is from token, rather than cookie
var accessToken = httpContext.Request.Headers["x-access-token"];
var security = new Security();
var decrypted = JsonConvert.DeserializeObject<TokenModel>(security.Decrypt(accessToken));
var clientip = GetClientIp(httpContext.Request);
if(httpContext.Request.Headers["x-client-ip"] == null)
{
return false;
}
if (httpContext.Request.Headers["x-client-ip"] != decrypted.Ip)
{
return false;
}
if (!IsSecretValid(decrypted))
{
return false;
}
MembershipUser u = Membership.GetUser(decrypted.UserId);
}
What I am asking is, How do I convert the membership into a Principle, in order to then let the rest of the code for roles etc to work.
IPrincipal user = httpContext.User;
if (!user.Identity.IsAuthenticated)
{
return false;
}
if (_usersSplit.Length > 0 && !_usersSplit.Contains(user.Identity.Name, StringComparer.OrdinalIgnoreCase))
{
return false;
}
if (_rolesSplit.Length > 0 && !_rolesSplit.Any(user.IsInRole))
{
return false;
}
Is this even possible, and if so how.

Answer 1

sorry, found a way through deep thought:
httpContext.User = new GenericPrincipal(new GenericIdentity(u.UserName), System.Web.Security.Roles.GetRolesForUser(u.UserName));
This should then enable my controller actions to pick up userid etc if needed.