feat(auth): add configurable MaxAge to auth cookies

[jld-adriano]

Tracking issue

Related to frequent re-authentication issues reported by users (flyte/grafana.heph sessions expiring quickly)

Why are the changes needed?

Users were experiencing frequent re-authentication prompts because auth cookies were created without MaxAge or Expires attributes. This made them session cookies that browsers could clear at any time (e.g., when closing the browser, or based on browser-specific session management policies).

By adding a configurable MaxAge to cookies, sessions can persist for a specified duration (e.g., matching the token lifespan of 168h), significantly reducing login frequency.

What changes were proposed in this pull request?

1. Added MaxAge field (type config.Duration) to CookieSettings struct
2. Added maxAge field to CookieManager struct to store the configured value
3. Updated NewSecureCookie function to accept a maxAge time.Duration parameter
4. When maxAge > 0, the cookie's MaxAge attribute is set accordingly
5. Updated all NewSecureCookie call sites to pass the configured maxAge
6. Updated tests to pass 0 for maxAge (backward compatible - session cookie behavior)

Important for reviewers: This PR only adds the capability. To enable persistent cookies, the helm values need to be updated separately to set cookieSettings.maxAge (e.g., 168h to match token lifespan).

How was this patch tested?

• Existing unit tests updated and passing (TestSecureCookieLifecycle, TestGetHTTPRequestCookieToMetadataHandler)
• Ran go test -v -run "TestSecureCookieLifecycle|TestGetHTTPRequestCookieToMetadataHandler" ./... in flyteadmin/auth

Labels

• added: New maxAge configuration option for auth cookies

Check all the applicable boxes

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

Human Review Checklist

• Verify config.Duration is the appropriate type for MaxAge field
• Confirm the maxAge > 0 condition handles edge cases correctly
• Check if any other cookie creation paths were missed
• Track helm values update as a follow-up task

---

Link to Devin run: https://app.devin.ai/sessions/6bf80d9947cd470cba4919b461a7176f
Requested by: carlos

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment and CI monitoring