code: func (policy *KeyPolicy) goodCurve(c elliptic.Curve) (err error) {
  	// Simply use a whitelist for now.
  	params := c.Params()
  	switch {
  	case policy.AllowECDSANISTP256 && params == elliptic.P256().Params():
  		return nil
  	case policy.AllowECDSANISTP384 && params == elliptic.P384().Params():
  		return nil
  	default:
  		return fmt.Errorf(fmt.Sprintf("ECDSA curve %v not allowed", params.Name))
  	}
  }
docs: // GoodCurve determines if an elliptic curve meets our requirements.