Active Task
Research and implement OAuth2 PKCE flow for mobile app
Progress
42%
Researcher
Searching OAuth2 PKCE specifications across 3 sources
Planner
Analyzing security requirements and flow architecture
Coder
Waiting for implementation plan from Planner
Critic
Waiting for code to review
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Researcher
Found RFC 7636 — PKCE is mandatory for public clients (mobile/SPA). The code_verifier must be 43-128 chars, using unreserved URI characters.
9:14:02
OAuth 2.1 draft makes PKCE required for ALL clients, not just public. We should implement it broadly. [RFC 7636] [OAuth 2.1 Draft]
9:14:18
Found 3 implementation patterns: plain, S256 transform, and custom. S256 is the only one recommended by spec.
9:14:45
Planner
Proposed flow: 1) Generate code_verifier (crypto random) 2) Compute code_challenge = SHA256(verifier) 3) Send challenge with auth request 4) Send verifier with token exchange
9:14:32
Architecture decision: Store code_verifier in secure storage (Keychain on iOS, EncryptedSharedPrefs on Android). Never transmit it until token exchange.
9:15:01
Coder
Waiting for Planner to finalize the storage approach. Ready to implement once architecture is confirmed.
9:15:10
Critic
Planner's flow looks correct but missing: What happens on code_challenge_method mismatch? Need error handling for unsupported method at the auth server.
9:15:22
Also: Researcher confirmed S256 only, but we should gracefully degrade to plain if server doesn't support S256. Spec allows it as fallback.
9:15:40
To implement OAuth2 PKCE for your mobile app, use the S256 code challenge method as specified in RFC 7636. Generate a cryptographically random code_verifier (43-128 chars), compute the SHA256 hash as the code_challenge, and store the verifier in platform-specific secure storage (Keychain/EncryptedSharedPrefs). Include error handling for unsupported challenge methods with a graceful fallback to plain. This approach is forward-compatible with OAuth 2.1 which mandates PKCE for all client types.