code: func (a *AuthServer) GenerateUserCerts(key []byte, username string, ttl time.Duration, compatibility string) ([]byte, []byte, error) {
  	user, err := a.Identity.GetUser(username)
  	if err != nil {
  		return nil, nil, trace.Wrap(err)
  	}
  	checker, err := services.FetchRoles(user.GetRoles(), a.Access, user.GetTraits())
  	if err != nil {
  		return nil, nil, trace.Wrap(err)
  	}
  	certs, err := a.generateUserCert(certRequest{
  		user:          user,
  		roles:         checker,
  		ttl:           ttl,
  		compatibility: compatibility,
  		publicKey:     key,
  	})
  	if err != nil {
  		return nil, nil, trace.Wrap(err)
  	}
  	return certs.ssh, certs.tls, nil
  }
docs: // GenerateUserCerts is used to generate user certificate, used internally for tests