code: func (a *LocalKeyAgent) AddKey(key *Key) (*agent.AddedKey, error) {
  	// save it to disk (usually into ~/.tsh)
  	err := a.keyStore.AddKey(a.proxyHost, a.username, key)
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  
  	// load key into the teleport agent and system agent
  	return a.LoadKey(*key)
  }
docs: // AddKey activates a new signed session key by adding it into the keystore and also
  // by loading it into the SSH agent