code: func (g *Cloud) AddSSHKeyToAllInstances(ctx context.Context, user string, keyData []byte) error {
  	ctx, cancel := cloud.ContextWithCallTimeout()
  	defer cancel()
  
  	return wait.Poll(2*time.Second, 30*time.Second, func() (bool, error) {
  		project, err := g.c.Projects().Get(ctx, g.projectID)
  		if err != nil {
  			klog.Errorf("Could not get project: %v", err)
  			return false, nil
  		}
  		keyString := fmt.Sprintf("%s:%s %s@%s", user, strings.TrimSpace(string(keyData)), user, user)
  		found := false
  		for _, item := range project.CommonInstanceMetadata.Items {
  			if item.Key == "sshKeys" {
  				if strings.Contains(*item.Value, keyString) {
  					// We've already added the key
  					klog.Info("SSHKey already in project metadata")
  					return true, nil
  				}
  				value := *item.Value + "\n" + keyString
  				item.Value = &value
  				found = true
  				break
  			}
  		}
  		if !found {
  			// This is super unlikely, so log.
  			klog.Infof("Failed to find sshKeys metadata, creating a new item")
  			project.CommonInstanceMetadata.Items = append(project.CommonInstanceMetadata.Items,
  				&compute.MetadataItems{
  					Key:   "sshKeys",
  					Value: &keyString,
  				})
  		}
  
  		mc := newInstancesMetricContext("add_ssh_key", "")
  		err = g.c.Projects().SetCommonInstanceMetadata(ctx, g.projectID, project.CommonInstanceMetadata)
  		mc.Observe(err)
  
  		if err != nil {
  			klog.Errorf("Could not Set Metadata: %v", err)
  			return false, nil
  		}
  		klog.Infof("Successfully added sshKey to project metadata")
  		return true, nil
  	})
  }
docs: // AddSSHKeyToAllInstances adds an SSH public key as a legal identity for all instances
  // expected format for the key is standard ssh-keygen format: <protocol> <blob>