Tools: Automating Authentication Flows in Go: Lessons from a Security Researcher’s No-Docs Approach

Understanding the Context and Challenge ## Building the HTTP Client ## Executing the Authorization Request ## Handling the Redirects and Extracting Authorization Code ## Exchanging the Authorization Code for Tokens ## Lessons Learned ## Final Thoughts ## 🛠️ QA Tip In the realm of security research, efficiency and precision are paramount, especially when experimenting with complex authentication flows. Recently, I encountered a scenario where I needed to automate OAuth2 authorization flows in Go, but with little to no documentation or official SDKs available. This challenging environment necessitated a deep understanding of protocol flows, meticulous HTTP handling, and secure token management. Here, I’ll share key insights and practical code snippets that illustrate how to approach automation of auth flows effectively in Go, even when documentation is scarce. Typically, OAuth2 flows involve redirecting a user agent to an authorization server, obtaining authorization codes, and exchanging them for tokens. Without guided documentation, the approach becomes exploratory: The core challenge is handling redirects, managing cookies, CSRF tokens, and dynamic parameters—all securely and reliably. In Go, a custom HTTP client with cookie management is essential to track sessions and handle redirects. This setup ensures that cookies and redirects are processed seamlessly. The authorization flow begins by constructing the correct URL with necessary parameters: Observe the responses, especially redirect URLs, tokens, and any hidden form parameters. Once redirected, the server response often includes a code in the URL. Parse this from the redirect URL: This step involves sending a POST request with form parameters: Handling the response allows secure storage of tokens, ready for subsequent API calls. Manual documentation gaps can hinder automation, but with a solid understanding of protocols, meticulous observation, and careful coding, automating auth flows in Go is achievable. This process emphasizes adaptability, security, and a deep grasp of underlying standards—lessons valuable for both security research and production implementations. This approach exemplifies how security research can lead to robust, adaptable solutions—an essential mindset for app security, automation, and protocol comprehension. Pro Tip: Use TempoMail USA for generating disposable test accounts. Templates let you quickly answer FAQs or store snippets for re-use. Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink. Hide child comments as well For further actions, you may consider blocking this person and/or reporting abuse CODE_BLOCK: import ( "net/http" "net/http/cookiejar" "log" ) func newClient() *http.Client { jar, err := cookiejar.New(nil) if err != nil { log.Fatal(err) } return &http.Client{ Jar: jar, CheckRedirect: func(req *http.Request, via []*http.Request) error { // handle redirects manually if necessary return nil }, } } Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: import ( "net/http" "net/http/cookiejar" "log" ) func newClient() *http.Client { jar, err := cookiejar.New(nil) if err != nil { log.Fatal(err) } return &http.Client{ Jar: jar, CheckRedirect: func(req *http.Request, via []*http.Request) error { // handle redirects manually if necessary return nil }, } } CODE_BLOCK: import ( "net/http" "net/http/cookiejar" "log" ) func newClient() *http.Client { jar, err := cookiejar.New(nil) if err != nil { log.Fatal(err) } return &http.Client{ Jar: jar, CheckRedirect: func(req *http.Request, via []*http.Request) error { // handle redirects manually if necessary return nil }, } } CODE_BLOCK: import ( "net/url" ) def startAuthFlow(client *http.Client, authEndpoint string, params map[string]string) (*http.Response, error) { query := url.Values{} for k, v := range params { query.Add(k, v) } authURL := authEndpoint + "?" + query.Encode() return client.Get(authURL) } // Example parameters params := map[string]string{ "client_id": "your-client-id", "redirect_uri": "https://yourapp.com/callback", "response_type": "code", "scope": "openid profile", "state": "randomStateString", } resp, err := startAuthFlow(client, "https://auth.example.com/authorize", params) Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: import ( "net/url" ) def startAuthFlow(client *http.Client, authEndpoint string, params map[string]string) (*http.Response, error) { query := url.Values{} for k, v := range params { query.Add(k, v) } authURL := authEndpoint + "?" + query.Encode() return client.Get(authURL) } // Example parameters params := map[string]string{ "client_id": "your-client-id", "redirect_uri": "https://yourapp.com/callback", "response_type": "code", "scope": "openid profile", "state": "randomStateString", } resp, err := startAuthFlow(client, "https://auth.example.com/authorize", params) CODE_BLOCK: import ( "net/url" ) def startAuthFlow(client *http.Client, authEndpoint string, params map[string]string) (*http.Response, error) { query := url.Values{} for k, v := range params { query.Add(k, v) } authURL := authEndpoint + "?" + query.Encode() return client.Get(authURL) } // Example parameters params := map[string]string{ "client_id": "your-client-id", "redirect_uri": "https://yourapp.com/callback", "response_type": "code", "scope": "openid profile", "state": "randomStateString", } resp, err := startAuthFlow(client, "https://auth.example.com/authorize", params) CODE_BLOCK: import "net/url" func extractCodeFromRedirect(resp *http.Response) (string, error) { redirectURL, err := resp.Request.URL.Parse(resp.Request.URL.String()) if err != nil { return "", err } code := redirectURL.Query().Get("code") return code, nil } Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: import "net/url" func extractCodeFromRedirect(resp *http.Response) (string, error) { redirectURL, err := resp.Request.URL.Parse(resp.Request.URL.String()) if err != nil { return "", err } code := redirectURL.Query().Get("code") return code, nil } CODE_BLOCK: import "net/url" func extractCodeFromRedirect(resp *http.Response) (string, error) { redirectURL, err := resp.Request.URL.Parse(resp.Request.URL.String()) if err != nil { return "", err } code := redirectURL.Query().Get("code") return code, nil } CODE_BLOCK: import ( "net/url" "strings" ) def exchangeCodeForToken(client *http.Client, tokenEndpoint, code string) (*http.Response, error) { data := url.Values{} data.Set("grant_type", "authorization_code") data.Set("code", code) data.Set("redirect_uri", "https://yourapp.com/callback") data.Set("client_id", "your-client-id") data.Set("client_secret", "your-client-secret") req, err := http.NewRequest("POST", tokenEndpoint, strings.NewReader(data.Encode())) if err != nil { return nil, err } req.Header.Set("Content-Type", "application/x-www-form-urlencoded") return client.Do(req) } Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: import ( "net/url" "strings" ) def exchangeCodeForToken(client *http.Client, tokenEndpoint, code string) (*http.Response, error) { data := url.Values{} data.Set("grant_type", "authorization_code") data.Set("code", code) data.Set("redirect_uri", "https://yourapp.com/callback") data.Set("client_id", "your-client-id") data.Set("client_secret", "your-client-secret") req, err := http.NewRequest("POST", tokenEndpoint, strings.NewReader(data.Encode())) if err != nil { return nil, err } req.Header.Set("Content-Type", "application/x-www-form-urlencoded") return client.Do(req) } CODE_BLOCK: import ( "net/url" "strings" ) def exchangeCodeForToken(client *http.Client, tokenEndpoint, code string) (*http.Response, error) { data := url.Values{} data.Set("grant_type", "authorization_code") data.Set("code", code) data.Set("redirect_uri", "https://yourapp.com/callback") data.Set("client_id", "your-client-id") data.Set("client_secret", "your-client-secret") req, err := http.NewRequest("POST", tokenEndpoint, strings.NewReader(data.Encode())) if err != nil { return nil, err } req.Header.Set("Content-Type", "application/x-www-form-urlencoded") return client.Do(req) } - Map out the protocol steps based on standards. - Use tools like curl or browser dev tools to observe real interactions. - Programmatically replicate these steps. - Always observe real flow interactions before automating. - Use robust cookie management to persist sessions. - Carefully parse URLs and response content to extract tokens. - Secure sensitive data; avoid hardcoding secrets. - Test thoroughly across different environments to handle edge cases. - OAuth 2.0 Authorization Framework (RFC 6749) - OAuth 2.0 Threat Model and Security Considerations - Go net/http package documentation