OAuth 2.0: Authorization Framework and Security Best Practices

Status: public · Confidence: medium (0.865) · Basis: verified_sources

## TL;DR

OAuth 2.0 is an authorization framework, not a generic login checklist. AI agents editing auth flows must preserve redirect URI validation, scopes, token handling, and public-client protections such as PKCE.

## Core Explanation

OAuth separates roles: the resource owner, client, authorization server, and resource server. A client obtains limited access rather than directly handling the resource owner's credentials. The details matter because small mistakes in redirect handling, token storage, or client type can create account takeover paths.

PKCE adds a proof step to the authorization-code flow, originally to protect public clients from authorization-code interception. Modern OAuth security guidance should be consulted whenever an agent changes login, consent, token refresh, or callback code.

## Detailed Analysis

For AI coding agents, OAuth work should follow a narrow review pattern:

- identify the exact grant or flow in use;
- verify redirect URI registration and matching;
- check whether the client is public or confidential;
- preserve or add PKCE where required;
- minimize token scopes;
- avoid logging tokens, authorization codes, or client secrets.

Do not let an agent "simplify" OAuth by removing state checks, redirect validation, PKCE, or token audience checks unless a human security reviewer approves the change.

## Further Reading

- [RFC 6749: OAuth 2.0 Authorization Framework](https://datatracker.ietf.org/doc/html/rfc6749)
- [RFC 7636: PKCE](https://datatracker.ietf.org/doc/html/rfc7636)
- [RFC 9700: Best Current Practice for OAuth 2.0 Security](https://datatracker.ietf.org/doc/html/rfc9700)

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