[docs] Service tokens documentation is misleading

[Jorge Merlino]

- [x] This doc is inaccurate in this way: It mentions that service_token_roles_required is optional but service tokens do not work well if it is disabled
- [ ] This is a doc addition request.
- [x] I have a fix to the document that I can paste below including example: input and output.

I think the note that says: "There is no configuration required for a service to receive service tokens" should be removed and we should move the service_token_roles_required explanation from troubleshooting to the configuration section and tell that it is mandatory to receive service tokens.

The problem that occurs when service_token_roles_required is not enabled is that keystonemiddleware do not validate expired user tokens unless the role verification has passed (see https://opendev.org/openstack/keystonemiddleware/src/branch/master/keystonemiddleware/auth_token/__init__.py#L403). Thus, if the role checking is not enabled, service tokens do not help when the user token is invalid even if they are not.

-----------------------------------
Release: 20.0.2.dev11 on 2019-07-22 12:51:47
SHA: c0437a03cfd34432c05a5b727899a3274f6ce725
Source: https://opendev.org/openstack/cinder/src/doc/source/configuration/block-storage/service-token.rst
URL: https://docs.openstack.org/cinder/yoga/configuration/block-storage/service-token.html

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/cinder/+/859853

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/cinder/+/859853
Committed: https://opendev.org/openstack/cinder/commit/850a58a29ca7f700559b69a41e885685228db6fa
Submitter: "Zuul (22348)"
Branch: master

commit 850a58a29ca7f700559b69a41e885685228db6fa
Author: Jorge Merlino <email address hidden>
Date: Thu Sep 29 10:39:25 2022 -0300

    Fix service token documentation

    Make clear that service_token_roles_required parameter is required for
    service tokens to work properly.

    Closes-Bug: #1991154
    Change-Id: I8293b48b3740ab3a22ac478ba2c0b80f57bb3761

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/cinder 22.0.0.0rc1 release candidate.