Dictionary<string, string> parameters = GetCustomParameters(company.Id);
Uri uri = new Uri(parameters["serviceUrl"]);
var username = parameters["username"];
var password = parameters["password"];
var entity = parameters["entity"];
ClientCredentials credentials = new ClientCredentials();
credentials.UserName.UserName = username;
credentials.UserName.Password = password;

OrganizationServiceProxy osproxy = new OrganizationServiceProxy(uri, null, credentials, null);
IOrganizationService _services = (IOrganizationService)osproxy;
QueryExpression query = new QueryExpression()
{
    EntityName = entity,
    ColumnSet = new ColumnSet("firstname", "lastname", "emailaddress")
};

EntityCollection retrieved = _services.RetrieveMultiple(query);