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

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.

Understanding the Context and Challenge

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:

• Map out the protocol steps based on standards.
• Use tools like curl or browser dev tools to observe real interactions.
• Programmatically replicate these steps.

The core challenge is handling redirects, managing cookies, CSRF tokens, and dynamic parameters—all securely and reliably.

Building the HTTP Client

In Go, a custom HTTP client with cookie management is essential to track sessions and handle redirects.

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
        },
    }
}

This setup ensures that cookies and redirects are processed seamlessly.

Executing the Authorization Request

The authorization flow begins by constructing the correct URL with necessary parameters:

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)

Observe the responses, especially redirect URLs, tokens, and any hidden form parameters.

Handling the Redirects and Extracting Authorization Code

Once redirected, the server response often includes a code in the URL. Parse this from the redirect URL:

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
}

Exchanging the Authorization Code for Tokens

This step involves sending a POST request with form parameters:

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)
}

Handling the response allows secure storage of tokens, ready for subsequent API calls.

Lessons Learned

• 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.

Final Thoughts

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.

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References:

• OAuth 2.0 Authorization Framework (RFC 6749)
• OAuth 2.0 Threat Model and Security Considerations
• Go net/http package documentation

This approach exemplifies how security research can lead to robust, adaptable solutions—an essential mindset for app security, automation, and protocol comprehension.

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