code: func (c *DiskTokenCache) GetToken(key *CacheKey) (*Token, error) {
  	cache, err := c.readCacheFile()
  	if err != nil {
  		return nil, err
  	}
  	for _, entry := range cache.Cache {
  		if EqualCacheKeys(&entry.Key, key) {
  			return &Token{
  				Token: entry.Token,
  				Email: entry.Email,
  			}, nil
  		}
  	}
  	return nil, nil
  }
docs: // GetToken reads the token from cache.