code: func (c *Client) UpsertToken(tok services.ProvisionToken) error {
  	_, err := c.PostJSON(c.Endpoint("tokens"), GenerateTokenRequest{
  		Token: tok.GetName(),
  		Roles: tok.GetRoles(),
  		TTL:   backend.TTL(clockwork.NewRealClock(), tok.Expiry()),
  	})
  	if err != nil {
  		return trace.Wrap(err)
  	}
  	return nil
  }
docs: // UpsertToken adds provisioning tokens for the auth server