docs: add OAUTH_AUTHORIZE_PARAMS env var documentation

[rndmcnlly]

Summary

• Documents the new OAUTH_AUTHORIZE_PARAMS environment variable in the SSO page and env-config reference
• This variable accepts a JSON object of extra query parameters appended to the OIDC authorization redirect URL
• Useful for OIDC brokers (CILogon, Keycloak, Dex) that support parameters to pre-select or restrict the upstream identity provider

Depends on

This docs PR depends on open-webui/open-webui#22867, which adds the feature to the codebase. Marking as draft per the docs contribution guidelines until that PR merges.

Files changed

• docs/features/access-security/auth/sso/index.mdx — added OAUTH_AUTHORIZE_PARAMS to the OIDC env var list (item 8, after OAUTH_AUDIENCE)
• docs/reference/env-configuration.mdx — added full reference entry with type, default, description, and examples table for common brokers

[pr-validator-bot]

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[rndmcnlly]

Human confirming: I'm targeting dev, here in draft mode because this documents a feature still in PR.