Why do organisations use OIDC instead of building custom authentication flows?

Why This Matters for Security Teams

OIDC matters because authentication logic becomes a security boundary, not just an application feature. When teams build custom login flows, they also inherit token handling, session lifecycle, federation trust, and error-prone edge cases that mature identity providers already solve. That increases the odds of inconsistent assurance, weak revocation, and fragmented audit trails across apps and environments. NHI Mgmt Group’s guide shows how credential sprawl and poor lifecycle control create real exposure, including the 90% of IT leaders who say properly managing NHIs is essential for a successful zero-trust implementation.

The practical issue is that custom auth flows often look simple during design but become difficult to secure once federation, MFA, token refresh, and delegated access are added. Standards-based identity reduces that complexity by separating authentication from application logic and making trust decisions more consistent. That is especially important in environments governed by NIST SP 800-53 Rev 5 Security and Privacy Controls, where identity assurance, logging, and access control must be repeatable. In practice, many security teams discover the weaknesses in custom auth only after a breach review forces them to reconstruct who issued what token, when, and for which app.

How It Works in Practice

OIDC sits on top of OAuth 2.0 and gives applications a standard way to verify identity using signed tokens from a trusted identity provider. The app does not need to store passwords or invent its own session rules. Instead, it validates the issuer, audience, expiry, and claims in the ID token, then maps those claims to local authorization rules. That is far safer than building bespoke code paths for login, password reset, MFA, and account linking.

For security teams, the main operational advantage is consistency. A single identity provider can enforce MFA, conditional access, device checks, and account lifecycle controls across many applications. This also supports better separation of duties, because the app consumes identity assertions rather than handling primary credentials directly. The result is less password sprawl and fewer places where secrets can leak. NHI Mgmt Group’s research on the OneLogin API Key Vulnerability shows why protecting federation secrets and signing material matters: if the trust anchor is exposed, every relying application inherits that risk.

• Use the identity provider for authentication and let applications only verify OIDC tokens.
• Validate issuer, audience, nonce, expiry, and signature on every token.
• Prefer short-lived tokens and rotate client secrets or private keys on a defined schedule.
• Log authentication events centrally so trust decisions can be audited across applications.
• Keep custom logic for application authorization, not for reinventing login.

These controls tend to break down in legacy apps that cannot support modern token validation or in highly distributed environments where teams cache tokens and trust claims longer than the token lifetime.

Common Variations and Edge Cases

Tighter federation controls often increase integration overhead, requiring organisations to balance usability against application compatibility. That tradeoff is real in legacy estates, embedded systems, and partner integrations where OIDC support is incomplete or where session handling was never designed for redirect-based flows. In those cases, current guidance suggests using OIDC at the edge where possible and isolating exceptions behind compensating controls rather than extending custom authentication patterns everywhere.

There is also a difference between authentication and authorization that teams sometimes blur. OIDC tells an application who the user is, but it does not replace RBAC, policy enforcement, or business logic. Custom flows still show up in niche cases such as device-bound authentication, air-gapped deployments, or protocols that cannot support browser redirects. Even then, the safest approach is to preserve standard token validation and avoid inventing proprietary claim formats or trust decisions. Standards such as ISO/IEC 27001:2022 Information Security Management reinforce the same principle: repeatable control design is stronger than one-off exceptions. The Twitter Source Code Breach illustrates how insecure internal handling can expose authentication secrets and undermine trust at scale, which is exactly what custom auth flows tend to amplify when they are rushed into production.

Related resources from NHI Mgmt Group

• When should organisations use self-signed TLS client authentication instead of CA-signed mTLS?
• When should organisations use three-factor authentication instead of 2FA?
• How should security teams govern authentication in applications that use OIDC flows?
• When should organisations use OIDC instead of plain OAuth?