code: function isValid ({accessToken, clientToken}) {
    return fetch(`${YGGDRASIL_API}/validate`, {
      method: 'POST',
      body: JSON.stringify({
        accessToken,
        clientToken
      }),
      headers: {
        'user-agent': USER_AGENT,
        'content-type': 'application/json'
      }
    })
      .then(handleErrors)
      .then(res => true)
      .catch(err => {
        if (err.message === 'Invalid token') return false
        throw err
      })
  }
docs: Checks if an access token is suitable for use with a Minecraft server.
  
  @param {Object} session - a session access token
  @param {string} session.accessToken - a session access token
  @param {string=} session.clientToken - must match the one used to obtain the access token
  @returns {Promise<boolean>} resolves true/false if token is valid/invalid
  @see {@link http://wiki.vg/Authentication#Validate}
  @example
  if (await mojang.isValid(session)) {
  console.debug('access token still good')
  } else {
  console.debug('access token has gone bad')
  }