code: func (a *AuthenticateSSHRequest) CheckAndSetDefaults() error {
  	if err := a.AuthenticateUserRequest.CheckAndSetDefaults(); err != nil {
  		return trace.Wrap(err)
  	}
  	if len(a.PublicKey) == 0 {
  		return trace.BadParameter("missing parameter 'public_key'")
  	}
  	certificateFormat, err := utils.CheckCertificateFormatFlag(a.CompatibilityMode)
  	if err != nil {
  		return trace.Wrap(err)
  	}
  	a.CompatibilityMode = certificateFormat
  	return nil
  }
docs: // CheckAndSetDefaults checks and sets default certificate values