Add config_flow helper to get reauth/reconfigure config entry (#127115)

* Add config_flow helper to get config entry from context

* Simplify

* Apply to aussie_broadband

* Another example

* Rename and adjust docstring

* Simplify

* Add test

* Refactor to hide context

* Raise

* Improve coverage

* Use AttributeError

* Use ValueError

* Raise UnknownEntry

homeassistant/config_entries.py

@@ -2726,6 +2726,36 @@ class ConfigFlow(ConfigEntryBaseFlow):
         """Return True if other_flow is matching this flow."""
         raise NotImplementedError
 
+    @property
+    def _reauth_entry_id(self) -> str:
+        """Return reauth entry id."""
+        if self.source != SOURCE_REAUTH:
+            raise ValueError(f"Source is {self.source}, expected {SOURCE_REAUTH}")
+        return self.context["entry_id"]  # type: ignore[no-any-return]
+
+    @callback
+    def _get_reauth_entry(self) -> ConfigEntry:
+        """Return the reauth config entry linked to the current context."""
+        if entry := self.hass.config_entries.async_get_entry(self._reauth_entry_id):
+            return entry
+        raise UnknownEntry
+
+    @property
+    def _reconfigure_entry_id(self) -> str:
+        """Return reconfigure entry id."""
+        if self.source != SOURCE_RECONFIGURE:
+            raise ValueError(f"Source is {self.source}, expected {SOURCE_RECONFIGURE}")
+        return self.context["entry_id"]  # type: ignore[no-any-return]
+
+    @callback
+    def _get_reconfigure_entry(self) -> ConfigEntry:
+        """Return the reconfigure config entry linked to the current context."""
+        if entry := self.hass.config_entries.async_get_entry(
+            self._reconfigure_entry_id
+        ):
+            return entry
+        raise UnknownEntry
+
 
 class OptionsFlowManager(data_entry_flow.FlowManager[ConfigFlowResult]):
     """Flow to set options for a configuration entry."""