auth: add new authentication source: GitHub, including GitHub Enterprise (#5340)

* Add new Authentication Source: GitHub, including GitHub Enterprise.

* Add vendor dependencies.

pkg/auth/github/github.go

@@ -0,0 +1,45 @@
+package github
+
+import (
+	"context"
+	"crypto/tls"
+	"errors"
+	"fmt"
+	"net/http"
+	"strings"
+
+	"github.com/google/go-github/github"
+)
+
+func GITHUBAuth(apiEndpoint, userName, passwd string) (string, string, string, string, string, error) {
+	tr := &http.Transport{
+		TLSClientConfig: &tls.Config{InsecureSkipVerify: true},
+	}
+	tp := github.BasicAuthTransport{
+		Username:  strings.TrimSpace(userName),
+		Password:  strings.TrimSpace(passwd),
+		Transport: tr,
+	}
+	client, err := github.NewEnterpriseClient(apiEndpoint, apiEndpoint, tp.Client())
+	if err != nil {
+		return "", "", "", "", "", errors.New("Authentication failure: GitHub Api Endpoint can not be reached")
+	}
+	ctx := context.Background()
+	user, _, err := client.Users.Get(ctx, "")
+	if err != nil || user == nil {
+		fmt.Println(err)
+		msg := fmt.Sprintf("Authentication failure! Github Api Endpoint authticated failed! User %s", userName)
+		return "", "", "", "", "", errors.New(msg)
+	}
+
+	var website = ""
+	if user.HTMLURL != nil {
+		website = strings.ToLower(*user.HTMLURL)
+	}
+	var location = ""
+	if user.Location != nil {
+		location = strings.ToUpper(*user.Location)
+	}
+
+	return *user.Login, *user.Name, *user.Email, website, location, nil
+}