Detecting OAuth 2.0 Endpoints with Nmap

Nmap is more than a port scanner—it is a precision tool for mapping and enumerating application infrastructure. When combined with targeted scripts, it can detect OAuth 2.0 flows, endpoints, and misconfigurations faster than manual inspection. This matters because OAuth 2.0 is often at the heart of authentication and API access. Weak configurations can expose tokens, leak scopes, or allow privilege escalation.

To find OAuth 2.0 surface area with Nmap, focus scans on HTTPS ports and REST API endpoints. Use nmap --script http-oauth (from NSE libraries) or custom Lua scripts to probe /authorize, /token, and /userinfo paths. Match response headers, JSON payloads, and status codes to confirm the presence and implementation of OAuth 2.0.

Key steps for effective OAuth 2.0 detection:

1. Service Discovery – Run nmap -p 443,8443,9443 <target> to narrow scope to likely API ports.
2. Endpoint Enumeration – Use NSE scripts to crawl discovery documents, such as .well-known/openid-configuration.
3. Token Handling – Capture and analyze token responses for expiration, scope, and audience.
4. Misconfiguration Checks – Look for open redirect URIs, insufficient TLS enforcement, or verbose error messages.

Security teams often miss OAuth 2.0 exposure in microservices or cloud environments. Nmap bridges that gap by automating reconnaissance at scale. Once identified, endpoints can be tested for compliance with RFC 6749 and related profiles. Checking the grant types available—authorization code, client credentials, device code—can reveal unnecessary risk.

Integrating Nmap OAuth 2.0 discovery into CI/CD pipelines turns endpoint detection into a continuous process. It reduces time-to-patch and ensures that new deployments do not weaken authentication. For production, encryption, minimal scope, and strict redirect validation are non-negotiable.

OAuth 2.0 remains secure only when its implementation is correct. Nmap’s flexibility makes it one of the fastest ways to know what’s exposed and where.

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