WIP: rfcs: new RFC on finer-grained role options

Release note: None

docs/RFCS/20200720_finer_grained_role_privileges.md

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+- Feature Name: Finer-grained Role Privileges
+- Status: draft
+- Start Date: 2020-07-21
+- Authors: Solon Gordon, Joel Kenny
+
+# Summary
+
+CockroachDB offers a built-in "admin" role which can be granted in order to
+give users a wide range of privileges. For one thing, it grants full
+permissions on all objects in the database. But there are also a number of
+operations which only admins are permitted to perform, like creating a new
+database or changing cluster settings. Since these operations can only be
+performed by admins, it's currently impossible to grant a user the ability to
+perform any one of these operations without giving them full admin access. This
+document proposes adding new role-level privileges so that admin-like abilities
+can be granted in a more fine-grained manner.
+
+# Motivation
+
+One major motivator for these changes is CockroachCloud. When we create the
+initial user for a CockroachCloud cluster, we currently grant the admin role
+to that user so they can perform basic operations like creating new databases.
+However, this also gives that user the ability to perform actions which could
+damage their cluster, like deleting the user which is used for automatic
+backup. Rather than granting the admin role, the CockroachCloud team would like
+the ability to create an "operator" role which only grants whatever abilities
+are necessary for the user to administer their cluster.
+
+These new options will also be useful for customers who want to grant users
+administrative abilities without managing the security of their cluster by
+limiting the number of people with true admin access.
+
+# Guide-level explanation
+
+As of v20.1, CockroachDB supports a few role-level options which can be granted
+via the `CREATE ROLE` or `ALTER ROLE` statement. One example is `CREATEROLE`,
+which grants users the ability to create, alter, and drop other roles. A
+complete list is available at
+https://www.cockroachlabs.com/docs/v20.1/alter-role.html#parameters.
+
+In order to support granting admin-like abilities, we add several new role
+options:
+
+### CREATEDB
+Allows a user to create new databases. The user who issues the command is
+granted all permissions on the database in question, emulating Postgres’
+behaviour of granting ownership of a database to the user who issues the
+`CREATE` call. This also confers the ability to rename a database via
+`ALTER DATABASE ...  RENAME`.
+
+### CREATELOGIN
+Allows a user to manage authentication. This grants access to:
+* the `WITH PASSWORD` clause for `CREATE/ALTER USER/ROLE`
+* the `VALID UNTIL` clause for `CREATE/ALTER USER/ROLE`
+* `ALTER USER/ROLE CREATELOGIN/NOCREATELOGIN`
+* `ALTER USER/ROLE LOGIN/NOLOGIN`
+
+Note that Raphael already has a PR for this:
+https://github.com/cockroachdb/cockroach/pull/50601
+
+### CREATEROLE
+As noted above, we already support this option. However, it currently does not
+prevent a non-admin user from dropping an admin. We will add this restriction
+so that an "operator" cannot drop essential admin users.
+
+### CONTROLJOB
+Allows a user to pause, resume, and cancel jobs. Non-admin users cannot control
+jobs created by admins.
+
+### CANCELQUERY
+Allows users to cancel queries of other users. Without this privilege, users
+can only cancel their own queries. Even with this privilege, non-admins cannot
+cancel admin queries.
+
+### CANCELSESSION
+Allows users to cancel sessions of other users. Without this privilege, users
+can only cancel their own session. Even with this privilege, non-admins cannot
+cancel admin sessions.
+
+### CHANGEFEED
+Allows users to run `CREATE CHANGEFEED` on tables they have `SELECT` privileges
+on. In the future this should also control whether a user can pause, resume, or
+cancel a changefeed, but that is currently controlled via job control so will
+be determined by the `CONTROLJOB` option.
+
+TODO(solon): Address how to make `RESTORE` and `IMPORT` available to non-admin
+users. Probably this should be determined by whether the user has the
+appropriate write access to the database or tables in question but we need to
+nail down the details.
+
+# Reference-level explanation
+The backend implementation of these new privileges should be straightforward.
+Role-level options are already stored in the `system.role_options` table and no
+migration is necessary to add new options. We will add the new privileges to
+our list of supported role options and assert that a user has the appropriate
+role option (or is an admin) when performing the associated operation.
+
+# Limitations
+
+## Automatic grants
+The new privileges proposed here do not include a way to guarantee that a role
+has privileges on all objects in the database. This remains a unique property
+of the admin role.
+
+In scenarios like CockroachCloud where a customer will not have access to an
+admin user, this could be undesirable since there will be no user who has
+reliable access to all objects. This could be mitigated by having a cron job
+which uses an admin user to grant the "operator" role access to all database
+objects, excepting those which are used for internal CockroachCloud processes.
+
+## Cluster settings
+Admins will still be the only users who can modify cluster-level settings. In
+the CockroachCloud use case, if there are cluster settings we want to allow
+users to change, we can make them available via the UI and rely on an internal
+admin user to perform the change.