[danilotrninic-db]

Summary

Address the three OAuth2 limitations described in #12512:

1. Increase the maximum response buffer size from 4 KiB to 64 KiB. The limit includes HTTP headers and the response body. The buffer still grows on demand.
2. Grow the JSON parser's token array on demand. Keep the initial capacity of 32 tokens and double it when needed, allowing responses with more fields or nested structures to be parsed.
3. Add optional oauth2.authorization_details and oauth2.authorization_details_file settings. They are mutually exclusive, and the configured value is sent as a form-body parameter on token requests. Files are read once during context initialization and reused on refresh.

The PR also fixes a pre-existing form-encoding issue found while adding authorization details. The URI encoder used for OAuth2 form values leaves literal & characters unescaped, but & separates fields in a form body. A value containing R&D, for example, can therefore be split into separate fields instead of reaching the server intact. The OAuth2 request builder now escapes & as %26 in all form values, covering both authorization_details and existing parameters.

Changes are limited to shared OAuth2 code and internal tests. Existing configurations require no changes.

Fixes #12512.

---

Testing

• Provide configuration examples for the new options (below and in oauth2-authorization-details.yaml).

• Provide debug-level test logs (captured in oauth2-debug-logs.txt).

• Provide Valgrind memory-check results (below).

• [N/A] Test binary/container packaging: no packaging changes.

• [N/A] Request the maintainer's ok-package-test label: no packaging changes.

Configuration

Set one of the following options within an existing OAuth2-enabled output. Replace the example JSON with the authorization details your provider accepts.

oauth2.authorization_details: |-
  [
    {
      "type": "example",
      "name": "R&D"
    }
  ]

Alternatively, store the JSON in a file and replace the inline setting with:

oauth2.authorization_details_file: /etc/fluent-bit/authorization-details.json

The options are mutually exclusive. Files are read once at context initialization.

Verification

Linux: 14 selected internal CTest suites and 8 HTTP/OpenTelemetry OAuth2 integration cases passed, including the integration cases under strict Valgrind.

100% tests passed, 0 tests failed out of 14
Total Test time (real) =   2.95 sec

Normal:   8 passed, 47 deselected in 52.97s
Valgrind: 8 passed, 47 deselected in 75.37s

Both flb-it-oauth2 and flb-it-oauth2_jwt also passed Valgrind and reported:

LEAK SUMMARY:
   definitely lost: 0 bytes in 0 blocks
   indirectly lost: 0 bytes in 0 blocks
     possibly lost: 0 bytes in 0 blocks
   still reachable: 112 bytes in 2 blocks
        suppressed: 0 bytes in 0 blocks
ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

The still-reachable allocations are from OpenSSL initialization.

Documentation

• These options need documentation updates (not included in this PR).

Backporting

• [N/A] Apply these changes to a stable release branch: this PR targets master.

---

Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

Summary by CodeRabbit

• New Features
  • OAuth2 configuration supports authorization details provided inline or from a file. The details are included in token requests. Configurations that provide both sources, or reference missing or empty files, are rejected.
• Bug Fixes
  • Improved token-response handling, including parsing responses with many token fields, reading only top-level token fields, and rejecting invalid or oversized responses.
  • Form values containing ampersands are now correctly escaped.
  • Token responses can now be read up to 64 KiB.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: defaults
• Review profile: CHILL
• Plan: Advanced
• Run ID: 3fd3b667-7a35-439b-917a-e7e6056b54f2

📥 Commits

Reviewing files that changed from the base of the PR and between cd8f0c8 and cfacc6d.

📒 Files selected for processing: 2

• src/flb_oauth2.c
• tests/internal/oauth2.c

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📝 Walkthrough

OAuth2 configuration accepts authorization details inline or from a file and includes them in token requests. The JSON response parser grows its token buffer with size checks and reads fields from the top-level object. Token requests use a 64 KiB response buffer.

Changes: OAuth2 token handling

Layer / File(s)	Summary
Configure and send authorization details include/fluent-bit/flb_oauth2.h, src/flb_oauth2.c, tests/internal/oauth2.c	OAuth2 configuration accepts mutually exclusive inline and file-based authorization details. Configuration cloning reads file contents, and token requests include the effective value as encoded form data. Tests cover initial and forced-refresh requests, file-backed values, and invalid configurations.
Grow JSON parsing and response capacity src/flb_oauth2.c, tests/internal/oauth2.c	The JSON parser grows its token array with input-size and allocation checks, and reads token fields only from the top-level object. Token requests use a 64 KiB response buffer. Tests cover parser growth, malformed and oversized input, nested fields, and response-size boundaries.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Feature · Severity of issue fixed: Medium

Sequence Diagram(s)

sequenceDiagram
  participant OAuth2Config
  participant flb_oauth2_config_clone
  participant oauth2_append_kv
  participant OAuth2HTTPClient
  participant TokenEndpoint
  OAuth2Config->>flb_oauth2_config_clone: provide inline value or file path
  flb_oauth2_config_clone->>flb_oauth2_config_clone: read file into effective value when configured
  flb_oauth2_config_clone->>oauth2_append_kv: provide authorization_details form value
  oauth2_append_kv->>OAuth2HTTPClient: return encoded request body
  OAuth2HTTPClient->>TokenEndpoint: send token request

Loading

Merge Risk: ⚪ Minimal · up to cfacc

The identified authorization-details encoding concern does not affect token requests, and no unresolved merge-blocking issue is established.

Security architecture risk: 🟡 Moderate · up to 12dc9

Deeply nested token responses can now consume excessive CPU and delay authentication. Exploitation requires control of the configured token server or interception of an unprotected connection. Response sizes remain capped, and configuration validation and form encoding provide important controls.

Retained concerns

• Medium · security · inferred: The larger response allowance and dynamic token growth admit deeply nested JSON that drives quadratic parser work while the authentication refresh lock is held. The previous 32-token limit rejected such responses early. A compromised token endpoint, or an interceptor where HTTP is configured, can therefore consume substantial CPU and delay users of the affected OAuth2 context despite the response-byte cap.

Security review details

Security Blast Radius

• inferred — The parser concern is reachable through token responses for shared OAuth2 consumers, not through the internal test functions classified as public entrypoints. Its directly supported scope is CPU consumption during refresh and delayed authentication for the affected context. Multiple contexts contacting a controlled issuer could inherit the condition, but deployment-wide or cross-tenant exposure is not established.

Security Findings and Attack Paths

• inferred — A responder controlling the configured token endpoint can return a small valid token object with an extra field containing tens of thousands of nested arrays. Dynamic growth allows parsing to reach their closing brackets, where repeated parent-chain walks produce quadratic work while refresh remains locked. The base parser exhausted its 32-token allocation before reaching this expensive phase. Exploitation and elapsed processing time were not measured.

Trust Boundaries and Controls

• observed — Authorization details originate in output configuration and enter a cloned OAuth2 context. Conflicting sources and file-read failures reject initialization, and the inspected production consumers propagate constructor failure. The loader reads file contents as text without local JSON-schema or path-policy enforcement.
• observed — The destination remains the configured token URL. Existing setup permits HTTP or HTTPS and initializes TLS verification for HTTPS; this PR does not add a separate destination or alter that transport selection. HTTPS limits interception but does not constrain responses from a compromised trusted issuer.

Resilience and Maintainability Implications

• observed — Initialization failures clean cloned configuration, destruction releases the authorization-details snapshot, and request-construction failures discard the incomplete body. These ownership controls contain partial initialization and allocation failures, but do not bound nested-response parsing work.

Hardening Proposals

• proposed — Bound JSON nesting or parsing work independently of response bytes, or use a closing-container implementation that avoids repeated walks from the last token. Preserve support for larger legitimate responses while preventing adversarial nesting from monopolizing refresh processing.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 27 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the two main changes: authorization details support and larger OAuth2 token responses.
Linked Issues check		[#12512] src/flb_oauth2.c sets the OAuth2 response buffer limit to 64 KiB. It grows the JSMN token array from 32 tokens on JSMN_ERROR_NOMEM and checks size and allocation limits. It adds mutually …
Out of Scope Changes check		The form-encoding change in src/flb_oauth2.c escapes & as %26 within every OAuth2 form value. This directly supports the required authorization_details form parameter and existing OAuth2 param…

Full details: Linked Issues check

Explanation

[#12512] src/flb_oauth2.c sets the OAuth2 response buffer limit to 64 KiB. It grows the JSMN token array from 32 tokens on JSMN_ERROR_NOMEM and checks size and allocation limits. It adds mutually exclusive inline and file settings, reads file content during configuration cloning, trims it, and reuses the cached value in token-request bodies. The tests cover response-size boundaries, token growth, invalid input, nested fields, inline and file settings, refresh reuse, and invalid configuration.

Full details: Out of Scope Changes check

Explanation

The form-encoding change in src/flb_oauth2.c escapes & as %26 within every OAuth2 form value. This directly supports the required authorization_details form parameter and existing OAuth2 parameters. The related tests use values containing &, %26, and +. No unrelated production changes are evident.

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Actionable comments posted: 1

---

• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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Inline comments:
Review comments at @src/flb_oauth2.c:
- Around line 310-327: In the authorization_details_file branch, reject content
that is missing or has zero length after flb_file_read; destroy dst and return
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---

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[danilotrninic-db]

Configuration example and test evidence:

• oauth2-authorization-details.yaml: examples of configuration using inline and file-based authorization details.
• oauth2-debug-logs.txt: complete OAuth2 suite results, Valgrind results, and representative debug-level integration logs.
  oauth2-authorization-details.yaml
  oauth2-debug-logs.txt

[danilotrninic-db]

Added a follow-up fix for a pre-existing response-parser issue. Nested fields in token responses could disrupt key/value traversal or overwrite top-level token values. The parser now processes only keys belonging to the root object.

Added regression coverage for nested authorization details preceding required fields and nested fields sharing the names of top-level token fields. Both cases fail before the fix and pass afterward. All focused internal and HTTP/OpenTelemetry OAuth2 integration tests pass, including the Valgrind checks.

[edsiper]

@codex review

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-22T13:54:26.882393Z	cfacc6d	Manual request

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Codex Review: Didn't find any major issues. 🚀

Reviewed commit: cfacc6db27

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