Reconcile ClientCreator and TransportManager

[jlewi]

The code base has started using two different mechanisms for handling auth credentials.
Palantir's Client Creator

Transport Manager

ClientCreator caches clients for different repositories
TransportManager caches different http transports from which clients can then be created.

You can extract the transport from the client's returned by ClientCreator e.g.

client.Client().Transport

https://github.com/google/go-github/blob/dff9dcc41c9c60c776df318d0938c1ad3dc2d2e4/github/github.go#L218

TransportManager is using
https://github.com/bradleyfalzon/ghinstallation to handle authenticating as a GitHubApp.

How does ClientCreator handle this?
Looks like its using ghinstallation as well
https://github.com/palantir/go-githubapp/blob/6c26ee49f52ddf0a2485d1c5f666b3dfda9ec8c1/githubapp/client_creator.go#L355

[jlewi]

So I think we could consolidate on ClientCreator and pass github.client arounds as needed. On the other hand github.client is a github V3 (REST client) and some of our code is using GitHub V4 (GraphQL). Seems a bit weird to obtain a V4 client from a V3 client.

[jlewi]

It looks like Palantir's clientcreator adds some functionality for setting up middleware.

[jlewi]

Here's an example of creating Palantir's ClientCreator

hydros/cmd/commands/server.go

Line 58 in aae0be5

config, err := app.BuildConfig(githubAppID, webhookSecret, privateKeySecret)

It uses a Config object to pass in the secret and other app configuration

hydros/pkg/app/config.go

Line 55 in aae0be5

config := &githubapp.Config{

[jlewi]

Palantir's ClientCreator takes an InstallationID to create a client.

We have the helper function

hydros/pkg/github/github.go

Line 17 in aae0be5

func GetInstallID(appID int64, privateKey []byte, owner string, repo string) (int64, error) {

TransportManager.Get

hydros/pkg/github/github.go

Line 104 in aae0be5

func (m *TransportManager) Get(org string, repo string) (*ghinstallation.Transport, error) {

Provides a convenient wrapper to get the InstallD for a given repository and then return the client for it.