Add clean HTTP client and improve token source

Introduces a cleanHTTPClient function for better HTTP client defaults and connection pooling. Updates NewInstallationTokenSource to use the new HTTP client and wraps the installationTokenSource with oauth2.ReuseTokenSource for improved token reuse.

Author: jferrl

auth.go

@@ -187,18 +187,24 @@ type installationTokenSource struct {
 func NewInstallationTokenSource(id int64, src oauth2.TokenSource, opts ...InstallationTokenSourceOpt) oauth2.TokenSource {
 	ctx := context.Background()
 
+	httpClient := cleanHTTPClient()
+	httpClient.Transport = &oauth2.Transport{
+		Source: oauth2.ReuseTokenSource(nil, src),
+		Base:   httpClient.Transport,
+	}
+
 	i := &installationTokenSource{
 		id:     id,
 		ctx:    ctx,
 		src:    src,
-		client: github.NewClient(oauth2.NewClient(ctx, src)),
+		client: github.NewClient(httpClient),
 	}
 
 	for _, opt := range opts {
 		opt(i)
 	}
 
-	return i
+	return oauth2.ReuseTokenSource(nil, i)
 }
 
 // Token generates a new GitHub App installation token for authenticating as a GitHub App installation.

http.go

@@ -0,0 +1,30 @@
+package githubauth
+
+import (
+	"net"
+	"net/http"
+	"runtime"
+	"time"
+)
+
+// cleanHTTPClient returns a new http.Client with clean defaults and connection pooling.
+// Implementation based on github.com/hashicorp/go-cleanhttp
+// Licensed under MPL-2.0: https://github.com/hashicorp/go-cleanhttp/blob/master/LICENSE
+func cleanHTTPClient() *http.Client {
+	return &http.Client{
+		Transport: &http.Transport{
+			Proxy: http.ProxyFromEnvironment,
+			DialContext: (&net.Dialer{
+				Timeout:   30 * time.Second,
+				KeepAlive: 30 * time.Second,
+				DualStack: true,
+			}).DialContext,
+			MaxIdleConns:          100,
+			IdleConnTimeout:       90 * time.Second,
+			TLSHandshakeTimeout:   10 * time.Second,
+			ExpectContinueTimeout: 1 * time.Second,
+			ForceAttemptHTTP2:     true,
+			MaxIdleConnsPerHost:   runtime.GOMAXPROCS(0) + 1,
+		},
+	}
+}