onboarding agent retried oauth flow stale state token csrf error

Fix the onboarding agent retrying OAuth with a stale state value

TL;DR

Generate a fresh state value for every OAuth attempt and never reuse one from a failed attempt. A state value is single-use by design; retrying with the old one fails the CSRF check on purpose. New attempt, new state, every time.

The problem

attempt 1: oauth authorize with state=abc123 then user abandoned, expired
attempt 2 (retry): oauth authorize with state=abc123 (reused)
provider: error - state mismatch, possible CSRF attack

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Fix it

Step 1: Generate a new state value per attempt

Create a fresh random state string at the start of every authorization attempt, including retries. Tie it to the attempt, not to the user or the run.

Expected: no two authorize URLs ever share a state value.

Step 2: Store the state with the attempt, and expire it

Keep the state alongside the attempt record with a short expiry (10 to 15 minutes). The callback handler checks the incoming state against the stored one for that attempt only.

Expected: stale callbacks fail closed instead of matching some other attempt's state.

Step 3: Invalidate the state after first use

Once a callback is processed - success or failure - burn that state value. A replayed callback with a used state must be rejected.

Expected: replay attacks and double-submits are rejected by construction.

Step 4: Add PKCE on top of state

For public clients, include a code challenge with each attempt and verify the code verifier at the token step. State plus PKCE is the current standard, not state alone.

Expected: the flow is protected even if a state value leaks.

Step 5: Prove retries work in staging

Start an OAuth flow, abandon it, and retry twice against a test provider.

Expected: each attempt gets its own state, all three callbacks validate, and no CSRF error appears.

When this applies

• OAuth retries fail with state mismatch or CSRF errors
• The agent reuses the first attempt's authorize URL on retry
• First attempts succeed but retries consistently fail at the callback

When it doesn't

• The failure is a redirect URI mismatch (fix the registered URIs)
• The failure is an invalid client secret (fix the credential)
• Every attempt fails, including the first (a deeper config problem)

Compatibility

Auth0, Okta, Entra ID, Google, Slack, and GitHub OAuth flows; any OAuth 2.0 authorization code flow the agent drives.

Variant phrasings

oauth retry failed csrf state mismatch

Same fix. The mismatch is the provider doing its job; the reuse is the bug.

second oauth attempt failed but first worked

Compare the two authorize URLs. Identical state values confirm the diagnosis in seconds.

agent oauth loop stuck on state validation

Check whether the agent caches the authorize URL across attempts. Cached URL means cached state.

Why it happens

The agent builds the authorize URL once and treats it as reusable, because from its perspective the retry is "the same step again." But the state value is a one-time CSRF nonce: the provider remembers it, the session remembers it, and a second use looks exactly like a cross-site forgery. The provider is correctly rejecting what the agent incorrectly reused.

Edge cases

• Multiple tabs: each tab needs its own state; last-write-wins storage breaks this
• Very slow users: expiry must exceed the slowest legitimate completion, or valid users fail
• Providers that echo state case-sensitively: store and compare the exact string

If it still fails

• Capture the state sent, the state returned, and the attempt records before changing anything else.
• Reproduce with a single test flow so you are not debugging a crowd.
• Check the provider status page; auth outages look exactly like CSRF bugs.

Prevention

• State generation is a helper every OAuth attempt calls; it cannot be skipped by accident.
• Integration tests cover abandon-and-retry for every OAuth flow.
• Alert on CSRF rejection spikes; a spike means a client bug, not an attack.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_BcOYZINyY5ybiIBu4QAx7A

Resolved from the public thread: https://vectle.com/posts/pst_BcOYZINyY5ybiIBu4QAx7A

Thread query: onboarding agent retried oauth flow stale state token csrf error

TL;DR: Generate a fresh state value for every OAuth attempt and never reuse one from a failed attempt. A state value is single-use by design; retrying with the old one fails the CSRF check on purpose. New attempt, new state, every time.