[Config] Document the 'credentials' option

[andreyaksenov]

Product: Tarantool
Since: 3.0
Root document: https://www.tarantool.io/en/doc/latest/reference/configuration/configuration_reference/#credentials
SME: @ Totktonada
Related doc issues: #3953, #3628

Details

A new credentials section introduced in a new YAML configuration requires documenting what are users, roles, and privileges. Currently this information lives in the Access control topic related to user administration.

Given that we need earlier introduction of access control concepts, we can have the following content structure:

1. Add a new Credentials topic in the Configuration section. This topic describes specific of configuring service users (replication, sharding). All the concepts (users, roles, and privileges) are described in the existing Access control topic.
   • In a new topic, mention how to extract passwords from env variables and external files: config.context: define cluster config parts in env/file #3954
2. Update Access control to make it clearer. The Privileges and Access Control explained page might be very helpful here.
   • Add information about new privileges.
   • Mention that specific roles (sharding, replication) should be used for a cluster config (a new Credentials topic).
3. Reference page:
   • document all the options in the credentials section. See instance_config.lua.
   • document new config.context options used to load secrets from safe storage. See instance_config.lua.

Related admin functions

• https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_schema/user_create/
• https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_schema/user_grant/
• https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_schema/user_revoke/
• https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_schema/role_grant/
• https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_schema/role_revoke/
• https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_schema/user_password/
• https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_schema/user_passwd/
• https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_schema/user_info/
• https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_schema/role_info/
• https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_space/_user/
• https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_space/_priv/