adding examples for app auth

README.md

@@ -121,7 +121,10 @@ GitHub Apps authentication can be provided by the [ghinstallation](https://githu
 package.
 
 ```go
-import "github.com/bradleyfalzon/ghinstallation"
+import (
+	"github.com/bradleyfalzon/ghinstallation"
+	"github.com/google/go-github/v41/github"
+)
 
 func main() {
 	// Wrap the shared transport for use with the integration ID 1 authenticating with installation ID 99.
@@ -137,6 +140,9 @@ func main() {
 }
 ```
 
+*Note*: In order to interact with certain APIs, for example writing a file to a repo, one must generate an installation token
+using the installation ID of the GitHub app and authenticate with the OAuth method mentioned above. See the examples.
+
 ### Rate Limiting ###
 
 GitHub imposes a rate limit on all API clients. Unauthenticated clients are

example/newfilewithappauth/main.go

@@ -0,0 +1,95 @@
+//Copyright 2021 The go-github AUTHORS. All rights reserved.
+//
+//Use of this source code is governed by a BSD-style
+//license that can be found in the LICENSE file.
+
+//newfilewithappauth demonstrates the functionality of GitHub's app authentication
+//methods by fetching an installation access token and reauthenticating to GitHub
+//with OAuth configurations.
+package main
+
+import (
+	"context"
+	"fmt"
+	"github.com/bradleyfalzon/ghinstallation"
+	"github.com/google/go-github/v41/github"
+	"golang.org/x/oauth2"
+	"io/ioutil"
+	"net/http"
+	"time"
+)
+
+func main() {
+
+	const gitHost = "https://git.api.com"
+
+	privatePem, err := ioutil.ReadFile("path/to/pem")
+	if err != nil {
+		panic(err)
+	}
+
+	itr, err := ghinstallation.NewAppsTransport(http.DefaultTransport, 10, privatePem)
+	if err != nil {
+		fmt.Printf("faild to create app transport: %v\n", err)
+	}
+	itr.BaseURL = gitHost
+
+	//create git client with app transport
+	client, err := github.NewEnterpriseClient(
+		gitHost,
+		gitHost,
+		&http.Client{
+			Transport: itr,
+			Timeout:   time.Second * 30,
+		})
+	if err != nil {
+		fmt.Printf("faild to create git client for app: %v\n", err)
+	}
+
+	installations, _, err := client.Apps.ListInstallations(context.Background(), &github.ListOptions{})
+	if err != nil {
+		fmt.Printf("failed to list installations: %v\n", err)
+	}
+
+	//capture our installationId for our app
+	//we need this for the access token
+	var installID int64
+	for _, val := range installations {
+		installID = val.GetID()
+	}
+
+	token, _, err := client.Apps.CreateInstallationToken(
+		context.Background(),
+		installID,
+		&github.InstallationTokenOptions{})
+	if err != nil {
+		fmt.Printf("failed to create installation token: %v\n", err)
+	}
+
+	ts := oauth2.StaticTokenSource(
+		&oauth2.Token{AccessToken: token.GetToken()},
+	)
+	oAuthClient := oauth2.NewClient(context.Background(), ts)
+
+	//create new git hub client with accessToken
+	apiClient, err := github.NewEnterpriseClient(gitHost, gitHost, oAuthClient)
+	if err != nil {
+		fmt.Printf("failed to create new git client with token: %v\n", err)
+	}
+
+	_, resp, err := apiClient.Repositories.CreateFile(
+		context.Background(),
+		"repoOwner",
+		"sample-repo",
+		"example/foo.txt",
+		&github.RepositoryContentFileOptions{
+			Content: []byte("foo"),
+			Message: github.String("sample commit"),
+			SHA:     nil,
+		})
+	if err != nil {
+		fmt.Printf("failed to create new file: %v\n", err)
+	}
+
+	fmt.Printf("file written: %v", resp.StatusCode)
+}