snowpick/session.go

package main

import (
	"context"
	"fmt"
	"io"
	"net/http"
	"regexp"
)

var gckPattern = regexp.MustCompile(`g_ck\s*=\s*'([a-f0-9]+)'`)

// Session holds the authentication state for a ServiceNow instance.
type Session struct {
	Target  string
	Token   string
	Cookies []*http.Cookie
}

// Bootstrap creates an unauthenticated session against a ServiceNow instance.
// It fetches /login.do to obtain the g_ck CSRF token and session cookies.
func Bootstrap(ctx context.Context, target string, client *http.Client) (*Session, error) {
	url := fmt.Sprintf("https://%s/login.do", target)

	req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
	if err != nil {
		return nil, fmt.Errorf("creating request: %w", err)
	}
	setHeaders(req)

	resp, err := client.Do(req)
	if err != nil {
		return nil, fmt.Errorf("fetching /login.do: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != 200 {
		return nil, fmt.Errorf("/login.do returned %d", resp.StatusCode)
	}

	body, err := io.ReadAll(io.LimitReader(resp.Body, 4<<20))
	if err != nil {
		return nil, fmt.Errorf("reading response body: %w", err)
	}

	match := gckPattern.FindSubmatch(body)
	if match == nil {
		return nil, fmt.Errorf("g_ck token not found in /login.do response (%d bytes)", len(body))
	}

	return &Session{
		Target:  target,
		Token:   string(match[1]),
		Cookies: resp.Cookies(),
	}, nil
}

func setHeaders(req *http.Request) {
	req.Header.Set("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.93 Safari/537.36")
	if vendorHeader != "" {
		req.Header.Set("X-Vendor", vendorHeader)
	}
}

// vendorHeader is set via -vendor flag for engagement tracking.
var vendorHeader string