Feature Type

Would make my life easier

Feature Description

google.STT and google.TTS (Google/Vertex Speech-to-Text and Text-to-Speech) only support authentication via credentials_info (a service-account-key dict),credentials_file (a path on disk), or google.auth.default() (environment-based ADC). There's no way to pass a google.auth.credentials.Credentials` object directly.

This is a problem for setups using Workload Identity Federation with custom credential providers, where credentials are obtained in memory and don't exist as files on disk.
RealtimeModel already accepts a credentials parameter, and every other Google client library (Secret Manager, Storage, Cloud SQL, etc.) accepts one too. STT and TTS should match — especially since both already build their underlying client with credentials=<object> internally (STT._create_client,
TTS._ensure_client); they just derive that object from a file first. The ask is to allow that object to be supplied directly.

Proposed change: add an optional credentials parameter to google.STT and google.TTS and pass it through to the underlying SpeechAsyncClient /TextToSpeechAsyncClient. Defaults to NOT_GIVEN, so no behavior change for existing callers.

Workarounds / Alternatives

Subclassing the plugin to override client creation, or serializing the in-memory credentials to a temporary file — both fragile and version-coupled.

Additional Context

Same request as the one already accepted for RealtimeModel (add a credentials parameter) — this extends that parity to the STT and TTS plugins in the same livekit-plugins-google package.