Setter For the Authentication Challenge.
Clients can chose to register their custom selectors to be invoked.
// register the client as delegate for this request
[SMPUserManager setAuthChallengeSelector:(authenticationNeededForRequest:)];
SMPUserManager* userManager = [SMPUserManager initializeWithConnection:clientConn];
[userManager registerUser:"username" password:@"password" error:&error isSyncFlag:NO];
...
}
-(void)authenticationNeededForRequest:(SDMHttpRequest*)request
{
//
}