Bind CIBA-issued access tokens to the DPoP proof key

[thiva-k]

Purpose

CIBA-issued access tokens were never sender-constrained. The DPoP proof presented when polling the token endpoint was fully validated, but the resulting key thumbprint never reached the token builder, so the access token was issued without a cnf.jkt claim. A client configured with DPoPBoundAccessTokens received a plain bearer token while appearing to be DPoP-bound, with no error surfaced. Refresh tokens were unaffected.

Approach

verifyDPoPProof already runs before grant dispatch and stores the verified thumbprint in the request context. The CIBA grant handler now reads it back via dpop.GetJkt(ctx) when building the access token, mirroring the authorization_code handler. GetJkt returns an empty string when no proof was verified, so non-DPoP clients are unaffected and no schema, store, or verification changes are needed.

Related Issues

• Fixes CIBA-issued access tokens are not DPoP-bound #4226

Related PRs

• N/A

Checklist

• Followed the contribution guidelines.
• Manual test round performed and verified.
• Documentation provided. (Add links if there are any)
  • Ran Vale and fixed all errors and warnings
• Tests provided. (Add links if there are any)
  • Unit Tests
  • Integration Tests
• Breaking changes. (Fill if applicable)
  • Breaking changes section filled.
  • breaking change label added.

Security checks

• Followed secure coding standards in WSO2 Secure Coding Guidelines
• Confirmed that this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets.

Summary by CodeRabbit

• Bug Fixes
  • CIBA-issued access tokens now correctly preserve the request’s DPoP binding.
  • Requests with valid DPoP proof receive DPoP-bound tokens, while requests without proof continue to receive bearer tokens.

[coderabbitai]

📝 Walkthrough

Walkthrough

CIBA access-token issuance now passes the polling request’s DPoP JKT to token construction. Tests cover both DPoP-bound tokens with proof and bearer tokens without proof.

Changes

CIBA DPoP binding

Layer / File(s)	Summary
Propagate DPoP context backend/internal/oauth/oauth2/granthandlers/ciba.go	The CIBA grant handler passes the request context’s DPoP JKT to AccessTokenBuildContext.
Validate token outcomes backend/internal/oauth/oauth2/granthandlers/ciba_test.go	Tests verify DPoP-bound token construction with proof and bearer-token construction without proof, along with resource resolution, request consumption, and successful responses.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: 🟡 Moderate · up to 4c432

The PR changes CIBA token issuance so valid DPoP proofs produce sender-constrained access tokens, while requests without proofs remain bearer tokens. The required authentication-flow documentation update is missing, so merge should wait until the relevant API documentation is updated.

Sequence Diagram(s)

sequenceDiagram
  participant PollingRequest
  participant CIBAGrantHandler
  participant AccessTokenBuilder
  PollingRequest->>CIBAGrantHandler: provide request context
  CIBAGrantHandler->>AccessTokenBuilder: pass DPoP JKT in AccessTokenBuildContext
  AccessTokenBuilder-->>CIBAGrantHandler: construct access token

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Possibly related PRs

• thunder-id/thunderid#3893: Propagates DPoP JKT into an OAuth access-token build context for another grant flow.
• thunder-id/thunderid#4166: Modifies the CIBA token-issuance path with resource-aware token logic.

Suggested reviewers: thamindudilshan, thumulaperera, senthalan

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly states that CIBA-issued access tokens are bound to the DPoP proof key.
Description check	✅ Passed	The description explains the problem, implementation, related issue, tests, and security checks; unchecked optional items do not make it incomplete.
Linked Issues check	✅ Passed	The changes satisfy issue #4226 by passing the verified DPoP JKT into CIBA access-token construction and testing bound and bearer outcomes.
Out of Scope Changes check	✅ Passed	The code and tests are limited to CIBA DPoP token binding and directly support issue #4226.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches 💡 1

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• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests

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Actionable comments posted: 1

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Inline comments:
In `@backend/internal/oauth/oauth2/granthandlers/ciba.go`:
- Line 234: Update docs/content/apis.mdx to document the CIBA token behavior
associated with DPoPJkt: a valid DPoP proof binds the access token through
cnf.jkt, while requests without a proof receive an unbound Bearer token.

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ℹ️ Review info

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Run ID: f7d034a5-66c9-4b5a-a6f7-96432554e334

📥 Commits

Reviewing files that changed from the base of the PR and between 9e3217d and 4c4323c.

📒 Files selected for processing (2)

• backend/internal/oauth/oauth2/granthandlers/ciba.go
• backend/internal/oauth/oauth2/granthandlers/ciba_test.go

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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