code: func (c *Client) AuthenticateSSHUser(req AuthenticateSSHRequest) (*SSHLoginResponse, error) {
  	out, err := c.PostJSON(
  		c.Endpoint("users", req.Username, "ssh", "authenticate"),
  		req,
  	)
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  	var re SSHLoginResponse
  	if err := json.Unmarshal(out.Bytes(), &re); err != nil {
  		return nil, trace.Wrap(err)
  	}
  	return &re, nil
  }
docs: // AuthenticateSSHUser authenticates SSH console user, creates and  returns a pair of signed TLS and SSH
  // short lived certificates as a result