code: func (confSrc *EnvConfigurationSource) GetConfigurationByKey(key string) (interface{}, error) {
  	confSrc.Lock()
  	defer confSrc.Unlock()
  	value, ok := confSrc.Configurations[key]
  	if !ok {
  		return nil, errors.New("key does not exist")
  	}
  
  	return value, nil
  }
docs: //GetConfigurationByKey gets required configuration for a particular key