OAuth2 error handling moved into the helper

As of Home Assistant Core 2026.10, the OAuth2 helper raises exceptions that config entry setup already understands, so integrations no longer translate OAuth2 failures themselves.

What changed

The OAuth2 exceptions now inherit from the config entry exception that describes what should happen, and carry a translated message from the homeassistant integration.

Exception	Also a	Result when uncaught
ImplementationUnavailableError	ConfigEntryNotReady	Setup is retried
UnknownImplementationError	ConfigEntryAuthFailed	Reauth flow starts
OAuth2TokenRequestError	ConfigEntryNotReady	Setup is retried
OAuth2TokenRequestTransientError	ConfigEntryNotReady	Setup is retried
OAuth2TokenRequestConnectionError	ConfigEntryNotReady	Setup is retried
OAuth2TokenRequestReauthError	ConfigEntryAuthFailed	Reauth flow starts

All of them are importable from homeassistant.exceptions and carry a translated user-facing message, so the integration does not need a strings.json entry for them.

Migration

-    try:
-        implementation = await async_get_config_entry_implementation(hass, entry)
-    except ImplementationUnavailableError as err:
-        raise ConfigEntryNotReady(
-            translation_domain=DOMAIN,
-            translation_key="oauth2_implementation_unavailable",
-        ) from err
+    implementation = await async_get_config_entry_implementation(hass, entry)

Also remove the now-unused oauth2_implementation_unavailable entry from the exceptions section of strings.json.

Catching ValueError around this call can go as well. UnknownImplementationError subclasses ValueError for backwards compatibility, so a ValueError handler silently downgrades it and discards the translated message.

Token requests

-    try:
-        await auth.async_get_access_token()
-    except OAuth2TokenRequestReauthError as err:
-        raise ConfigEntryAuthFailed from err
-    except OAuth2TokenRequestError as err:
-        raise ConfigEntryNotReady from err
+    await auth.async_get_access_token()

The same applies to await session.async_ensure_token_valid().

Quality scale

The test-before-setup rule accepts await session.async_ensure_token_valid() in async_setup_entry as satisfying the rule, alongside await coordinator.async_config_entry_first_refresh(). Both raise the appropriate config entry exception on the integration's behalf.

When to keep catching

Central handling is a default, not a restriction. Keep an explicit handler when the integration genuinely needs different behavior, for example:

• Treating a specific status as permanent with ConfigEntryError instead of retrying.
• Adding context to the message that only the integration knows.
• Cleaning up integration state before the exception propagates.

In those cases, catch the most specific exception that applies and let the rest propagate.