fix(oauth): add User-Agent header to Reddit token refresh

[majiayu000]

Summary

• Add User-Agent header to Reddit OAuth token refresh requests
• Reddit API requires User-Agent header for all requests, including token refresh
• Without this header, requests fail with 403 error after initial token expires

Test plan

• [x] Added test to verify User-Agent header is included in Reddit OAuth requests
• [x] All existing OAuth tests pass (23 tests)

Fixes #1822

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[greptile-apps[bot]]

Greptile Summary

This PR fixes Reddit OAuth token refresh failures by adding the required User-Agent header to Reddit API requests. Reddit's API blocks requests without a User-Agent header with a 403 error, which was causing token refresh failures after the initial token expired.

Key Changes:

• Added User-Agent: sim-studio/1.0 (https://github.com/simstudioai/sim) header to Reddit OAuth configuration
• Added test coverage to verify the User-Agent header is included in Reddit OAuth requests
• Added Helm chart flexibility for custom network egress rules (unrelated infrastructure enhancement)

The implementation correctly leverages the existing additionalHeaders mechanism that's already used for GitHub's Accept header, ensuring consistency with the codebase patterns.

Confidence Score: 5/5

• This PR is safe to merge with no risk - it's a minimal, well-tested bug fix
• The fix directly addresses a documented Reddit API requirement, uses existing patterns (additionalHeaders), includes proper test coverage, and makes no breaking changes. The networkpolicy.yaml change is a safe infrastructure enhancement.
• No files require special attention

Important Files Changed

Filename	Overview
apps/sim/lib/oauth/oauth.ts	Added User-Agent header to Reddit OAuth configuration to fix 403 errors during token refresh
apps/sim/lib/oauth/oauth.test.ts	Added test to verify User-Agent header is included in Reddit OAuth requests
helm/sim/templates/networkpolicy.yaml	Added support for custom egress rules configuration through Helm values

Sequence Diagram

sequenceDiagram
    participant Client
    participant OAuthLib
    participant Reddit API
    
    Client->>OAuthLib: refreshOAuthToken('reddit', refreshToken)
    OAuthLib->>OAuthLib: getProviderAuthConfig('reddit')
    Note over OAuthLib: Creates config with<br/>User-Agent header
    OAuthLib->>OAuthLib: buildAuthRequest(config, refreshToken)
    Note over OAuthLib: Adds headers:<br/>- Content-Type<br/>- User-Agent (NEW)<br/>- Authorization (Basic Auth)
    OAuthLib->>Reddit API: POST /api/v1/access_token<br/>with User-Agent header
    alt Success
        Reddit API-->>OAuthLib: {access_token, expires_in}
        OAuthLib-->>Client: {accessToken, expiresInSeconds}
    else Failure (403 without User-Agent)
        Reddit API-->>OAuthLib: 403 Forbidden
        OAuthLib-->>Client: null
    end

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Project	Deployment	Review	Updated (UTC)
docs	Ready	Preview, Comment	Dec 22, 2025 5:52pm

[waleedlatif1]

@majiayu000 do you mind rebasing so the branch only has your commit

[majiayu000]

Done! Rebased onto the latest staging branch.