fix(frontend): include basePath in AUTH_OIDC_BASE_URL

[waterponey]

Summary

• When global.basePath.enabled is true, AUTH_OIDC_BASE_URL now includes the frontend base path (e.g. https://example.com/datahub instead of https://example.com)
• Adds an explicit oidcAuthentication.oidcBaseUrl override for cases where the auto-constructed URL is not suitable

Problem

AUTH_OIDC_BASE_URL was hardcoded to https://<ingress-host>, ignoring global.basePath.frontend. When deploying DataHub behind a base path (e.g. /datahub), the OIDC redirect_uri sent to the identity provider was missing the base path, causing authentication to fail with "Invalid parameter: redirect_uri".

Changes

charts/datahub/subcharts/datahub-frontend/templates/deployment.yaml
AUTH_OIDC_BASE_URL now uses a 3-way conditional:

1. If oidcAuthentication.oidcBaseUrl is set → use it verbatim
2. Else if global.basePath.enabled → append global.basePath.frontend to the ingress host
3. Else → ingress host only (existing behavior, no breaking change)

charts/datahub/subcharts/datahub-frontend/values.yaml
Added a commented oidcBaseUrl option in the oidcAuthentication block.

Test plan

• helm template with basePath.enabled=true and basePath.frontend=/datahub → AUTH_OIDC_BASE_URL is https://example.com/datahub
• helm template without basePath → AUTH_OIDC_BASE_URL is https://example.com (no regression) - [ ] helm template with explicit oidcBaseUrl → value is used as-is
• Deploy with OIDC + basePath and verify the callback URL matches the IdP configuration

Closes #680

Checklist

• The PR conforms to DataHub's Contributing Guideline (particularly Commit Message Format)
• Links to related issues (if applicable)
• Tests for the changes have been added/updated (if applicable)
• Docs related to the changes have been added/updated (if applicable)

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Note

Medium Risk
Changes how the frontend computes AUTH_OIDC_BASE_URL, which can affect OIDC redirect URIs and login behavior if misconfigured. Scope is limited to Helm templating/values and should be low impact for deployments not using OIDC or global.basePath.

Overview
Fixes OIDC deployments behind a base path by updating the frontend chart to include global.basePath.frontend when constructing AUTH_OIDC_BASE_URL.

Adds an oidcAuthentication.oidcBaseUrl values override to allow explicitly setting the redirect base URL, and bumps the parent Helm chart version to 0.8.23.

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[RyanHolstien]

Thanks for the contribution! 😄