How to Run Penetration Tests on Social Login and OAuth Flows to Prevent Account Takeovers

Stop account takeovers before they start: a practical pentest guide for OAuth and social login in municipal services

Hook: Municipal apps increasingly use social login and OAuth to simplify citizen access — but that convenience makes account takeover attacks an attractive, high-impact target for malicious actors. In late 2025 and early 2026, mainstream reporting highlighted surges in social-platform attacks that exploited authentication and reset flows. If you run or integrate public-facing city services, this guide gives a prioritized, step-by-step penetration testing checklist and concrete test cases to find and fix OAuth, token replay, and account-linkage weaknesses before attackers do.

Why this matters now (2026 context)

Across government technology projects in 2026, teams are accelerating use of OAuth/OIDC and social providers (Google, Apple, Facebook/Meta, LinkedIn) to lower friction for residents. That trend coincides with a wave of account takeover activity on major platforms reported in early 2026 — a reminder that attacker interest and scale are both rising. Municipal services are attractive because successful takeovers can expose sensitive PII, permit benefits fraud, or undermine civic trust.

Late 2025–early 2026 reporting showed large-scale attacks leveraging authentication flows to harvest or hijack accounts, underlining the need for targeted OAuth testing in civic systems.

Given constrained developer resources and regulatory pressure on citizen data privacy, a focused pentest program that targets OAuth, social login, token replay, and account-linkage is the highest-leverage security effort you can run this quarter.

Overview: What this guide covers

• A prioritized, step-by-step pentest checklist for OAuth/OIDC and social logins.
• Concrete test cases for token replay, refresh token abuse, client misconfiguration, redirect_uri and state handling, PKCE weaknesses, and account linkage errors.
• Tools, scripts and data points you can copy into Burp, Postman, or CI-based security tests.
• Remediation prioritization and reporting templates tailored to municipal teams and SaaS integrators.

High-level approach (inverted pyramid)

Start with the highest-risk, high-impact scenarios: token replay and account linkage checks that can lead to immediate account control. Then validate core OAuth/OIDC security controls and configuration. Finally, test secondary flows (password-reset, email linking, device flows) and operational resilience (revocation, key rotation).

Phases at a glance

1. Reconnaissance: Discover endpoints, clients, and social providers used by the app.
2. Threat modeling: Map how social identity maps to municipal accounts.
3. Automated checks: Verify common misconfigurations and weak attributes.
4. Manual exploitation: Target token replay, account linkage, and redirect flaws.
5. Post-exploit validation: Test revocation, session invalidation, and logging.
6. Reporting & remediation: Prioritize fixes and produce developer-oriented remediation steps.

Step-by-step pentest checklist (detailed)

1. Reconnaissance: inventory and mapping (quick wins)

• Locate OAuth endpoints and social providers by inspecting network traffic, HTML source, and mobile app code (decompile APK/IPA if permitted).
• Enumerate client IDs and redirect_uris in JS bundles, mobile code, or public metadata (/.well-known/openid-configuration).
• Gather scopes requested for each provider and confirm whether optional scopes like email or profile are required.
• Check third-party SDK versions in package manifests — outdated SDKs are common attack vectors in municipal apps.

2. Threat modeling: account linkage and attack paths

Map how an OAuth token (or social identity) becomes a municipal account. Common patterns include:

• Automatic account creation on first social login (link by email)
• Linking local accounts with social accounts via an account settings page
• Backend matching by email, phone, or external ID

Every mapping rule is a potential confusion point. Flag rules that automatically link by email without verification as high risk.

3. Automated configuration checks (use first to triage)

• Validate that state parameter is used and unpredictable for all authorization code flows.
• Ensure PKCE is required for public clients (native/mobile/SPAs).
• Confirm redirect_uris are not wildcarded and are validated server-side.
• Check token lifetimes for access and refresh tokens — long-lived tokens deserve closer scrutiny.
• Inspect ID token claims: aud, iss, exp, nbf, azp — and verify signature and alg.
• Verify HTTPS enforced, HSTS present, and secure SameSite cookie flags for session cookies.

4. Manual exploit test cases (high-value)

The following test cases are prioritized for municipal services and integration patterns.

Token replay and reuse

1. Capture an access or ID token during a legitimate login. Attempt reuse against APIs from a different client, origin, IP, or device. Expected secure behavior: token should be scoped tightly and fail when used from unexpected client context or when audience mismatch occurs.
2. Test refresh token replay: use the same refresh token concurrently from two different clients or devices. If refresh tokens are single-use, the second attempt should be rejected.
3. Practical test (curl):

   <code>curl -H "Authorization: Bearer <access_token>" https://api.city.example.gov/user/me</code>

   If this returns user data from a stolen token, flag as critical unless allowed by policy and mitigated by IP/session checks.

Authorization Code interception and PKCE checks

• Attempt to intercept an authorization code via a malicious redirect_uri or open redirect on the relying party. Confirm provider enforces pre-registered redirect_uris.
• Test PKCE: if the client is public (SPA/native), confirm the authorization server requires PKCE and rejects requests without a correct code_verifier.

State parameter CSRF

• Attempt authorization code flow without a state or with a predictable state value. Verify the app detects mismatch when the state is missing, reused, or predictable.

Redirect URI manipulation and open redirectors

• Test redirect_uris with additional query strings, path traversal, or URL-encoded payloads to find weak comparisons. Registered redirect URIs must be exact or follow strict rules.
• Scan the application for open redirectors (e.g., /redirect?next=) and test chaining to social provider redirect to capture tokens or codes.

Account linkage and social-login confusion

1. Confirm the process for linking a social profile to an existing municipal account. Test attacker scenarios such as: signing up with a Social account that matches an existing email, then using the provider-controlled email change/verification to take over municipal account.
2. Test edge case: social provider returns an email that’s not verified — does the relying party treat it as authoritative?
3. Attempt to create two accounts (local and social) that resolve to the same internal identifier (e.g., hashed email) and check whether the system merges or replaces identities improperly.

Scope and permission escalation via token manipulation

• Modify request parameters to request higher scopes (if possible) and confirm server-side enforcement of granted scopes vs requested scopes.
• Test JWT claim tampering: change exp, aud, or sub in an unsigned JWT or attempt alg=none attack. Verify server verifies signatures using the issuer’s current JWKS and respects alg restrictions.

Implicit and hybrid flow checks (legacy flows)

Many municipal integrations still rely on legacy flows. Test whether the implicit/hybrid flows leak tokens in browser histories, referrers, or logs. If present, recommend migrating to authorization code + PKCE.

Device and passwordless flows

• Test device code flow for polling-based brute-force or rate-limit bypasses.
• For email-based sign-in flows, confirm single-use links expire, are bound to client context, and cannot be replayed after first use.

Operational checks: revocation, rotation, logging

• Verify token revocation endpoints work and that revocation immediately invalidates access for active sessions.
• Validate JWKS key rotation is handled and old keys are expired; test signature verification against stale keys.
• Confirm authentication and token events are logged with sufficient fidelity (client_id, ip, user_agent, event_type) for incident response.

Concrete test cases you can run this week

Below are modular test cases with expected outcomes and remediation hints. Use them in Burp Suite, Postman, or an automated CI test harness.

Test case: Token replay from different origin

Steps:

1. Authenticate through normal flow and capture an access token.
2. From another environment (different IP/origin), call a protected API using the same token.

Expected secure result: token usage should fail if the server binds token to client context (mutual TLS, DPoP, or audience checks) or flags suspicious IP changes for high-risk operations. If success is allowed, ensure compensating controls exist (short expiry, step-up auth for sensitive ops).

Test case: Authorization code theft via open redirect

Steps:

1. Find a redirector on the relying party that forwards to an arbitrary URL.
2. Initiate OAuth flow with redirect_uri pointing to the redirector that resolves to an attacker-controlled endpoint.
3. Intercept the authorization code on that endpoint.

Expected secure result: provider only allows pre-registered redirect_uris and the relying party performs server-side validation; any interception attempt must fail to exchange the code without correct client secret or PKCE code_verifier.

Test case: Account takeover via email linking

Steps:

1. Create a municipal account A using email user@example.com (local password).
2. Create a social account B using the same email but without provider email verification (or with provider-verified email if the provider account is later compromised).
3. Login via social provider to the municipal app and observe whether the app auto-links or asks for confirmation.

Expected secure result: relying party should require explicit confirmation and multi-factor verification before linking. Linking by email alone should be denied unless email is verified and user interaction confirms intent.

Tools and commands

• Burp Suite + OAuth extension for intercepting flows and automating tests.
• mitmproxy for mobile app traffic capture.
• jq + curl for quick token replay tests: curl -H "Authorization: Bearer <token>" ...
• jwt.io / jose or python-jose for token decoding and signature verification.
• OIDC discovery endpoints: retrieve /.well-known/openid-configuration and JWKS to validate server settings.

Prioritizing findings and practical remediation

Not all findings are equal. Use this triage matrix tailored for municipal teams:

• Critical — Token replay (access to PII), account takeover via auto-linking, public client without PKCE, implicit flows exposing tokens.
• High — Missing state checks, wildcard redirect_uris, refresh tokens not rotated or single-use, insecure token storage in mobile apps.
• Medium — Long token lifetimes for low-risk APIs, incomplete logging, missing HSTS on auth endpoints.
• Low — Minor metadata inconsistencies, less-sensitive scope misconfigurations.

Remediation checklist (developer-friendly)

1. Enforce authorization code flow + PKCE for public clients; migrate away from implicit flow.
2. Require provider-verified email before auto-linking; make linkage explicit and require re-authentication for sensitive actions.
3. Implement single-use refresh tokens or rotate refresh tokens on use; limit refresh token scope and lifetime.
4. Reject wildcard redirect_uris and require exact matching; implement allowlist checks server-side.
5. Use DPoP or sender-constrained tokens for high-risk APIs; short-lived access tokens with refresh on server-side grant are ideal.
6. Log and monitor auth events (login, token issuance, token revocation) and pipe to SIEM for anomaly detection.
7. Document and test JWKS rotation procedures; validate signature verification and alg enforcement.

Case study (anonymized): city.gov platform

Example: a medium-sized city adopting social login discovered during a fifth-day pentest that the application auto-linked social logins by email without a verification step. An attacker who gained control of a social account via a separate platform attack could immediately access municipal services. The fix involved adding a mandatory confirmation dialog requiring the pre-existing municipal account password or 2FA when linking, and enforcing provider-verified email. Post-fix, retesting showed no path to takeover via social identity alone.

Operationalizing these tests in CI and release cycles

Make OAuth-specific tests part of your regular security pipeline:

• Automate /.well-known and JWKS checks as part of CI linting.
• Include token replay smoke tests that run against staging before release.
• Run a targeted manual pentest for major releases, changes in identity provider, or when adding new account-linkage logic.

2026 trends & future-proofing

Expect these trends to shape OAuth testing in 2026 and beyond:

• Increased use of sender-constrained tokens (DPoP, mTLS) for sensitive APIs.
• Broader adoption of FIDO2 and passkeys which change account-linkage models; pentesters must test fallback and recovery flows.
• Greater attacker focus on secondary flows (password reset, email linking) as social platforms harden primary auth — public reporting from early 2026 shows attackers adapting to reset/link avenues.
• More regulation and privacy scrutiny for public sector identity data; expect auditors to require evidence of secure OAuth practices.

Reporting: how to present findings to municipal stakeholders

Translate technical findings into operational impact:

• Start reports with a one-paragraph executive summary: risk, affected services, immediate mitigation required.
• Provide a developer remediation checklist with code-level examples or configuration snippets.
• Assign remediation priorities and provide an estimated timeline and testing steps for verification.

Quick-reference: must-test scenarios (printable list)

• Token replay from new origin — attempt API access.
• Refresh token reuse and rotation behavior.
• Authorization code interception via redirector/open redirect.
• PKCE enforcement for public clients.
• State parameter presence and unpredictability.
• Account-linkage confirmation and verified-email enforcement.
• JWT signature validation and alg enforcement.
• Revocation propagation and logging verification.

Actionable takeaways

• Prioritize token replay and account-linkage tests — these produce the fastest reduction in takeover risk for municipal services.
• Require PKCE and authorization-code flow for public clients; eliminate implicit flows.
• Never auto-link identities by email alone — always require explicit user action and verification.
• Automate discovery checks for /.well-known and JWKS as part of CI to catch configuration drift.

Next steps & resources

Start by running the reconnaissance checklist this week against your staging environment. If you need an immediate tactical playbook, copy the manual test cases into a Burp project and run them during your next sprint.

For up-to-date threat context, review public reporting on social-platform takeover waves (early 2026) and include those trends in your threat model: attackers are increasingly weaponizing password reset and social-account recovery flows.

Call to action

If you manage municipal integrations or developer docs for public services, schedule a dedicated OAuth pentest within the next 30 days. Need help operationalizing tests or remediating findings? Contact our civic-security team for an on-site workshop, or download our OAuth pentest checklist bundle to run in your CI pipeline.

Protect citizen accounts now — because a single social-login flaw can put hundreds or thousands of residents at risk.

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