Originally, the "extra" in token data is generated by auth plugin
and then will be return to users within token data.
In Kilo, the "extra" in token data was deprecated[1], after that
if the auth plugin generate the "extra", a warning log will be
raised. To stop the warning, the auth plugins should stop
generating "extra" field.
After two releases, in Mitaka, the "extra" in token data was
removed[2], but the "extra" was still created by default as an
empty dict {}. Actually, "extra" should not be created any more
in Mitaka because Keystone has warned the auth plugins for two
releases.
Now in Rocky, it's safe enough to remove the "extra" from token
issue flow at all since it has never been used from Mitaka. The
only concern for the out tree plugins about the removal is that
if they still put "extra" into auth_context, Keystone will raise
KeyError. But can it be happened? Only if the out tree plugins
ignore the warning in Kilo, and still contain "extra" but never
use them from Mitaka. For most auth plugins which follow the
Keystone deprecation step, this patch is a silent change.
[1]: https://review.openstack.org/#/c/162662
[2]: https://review.openstack.org/#/c/249480
Change-Id: I828cc0ad3ac265abdfea2e1571806add128ae51e
203787c37f