/// <summary>
/// Validate a user's login credentials and retrieve their info with their roles
/// </summary>
/// <param name="auth"></param>
/// <param name="model"></param>
/// <param name="log"></param>
public static Task <Maybe <AuthUserModel> > ValidateUserAsync(IAuthDataProvider auth, SignInModel model, ILog log)
{
log.Vrb("Validating credentials for {User}.", model.Email);
return(from _ in auth.ValidateUserAsync <AuthUserModel>(model.Email, model.Password)
from user in auth.RetrieveUserWithRolesAsync <AuthUserModel, AuthRoleModel>(model.Email)
select user);
}