Advanced concepts

Assignable permissions

Advanced actions

From a permissions standpoint, all actions take place against directly implemented or abstract types. There may be actions that are only implemented by some concrete types (e.g., not all auth-method implementations support a change-password action), but the permissions model still defines these capabilities at the abstract type level. This helps keep the overall system relatively simple and predictable.

Subactions

Some subactions are supported. These actions have a format top_level_action:subaction, such as read:self. Being granted the top level action infers being granted all subactions. Thus, if a grant conveys read, it also matches the API actions read and read:self. However, if a grant conveys read:self, it will match the API action read:self but will not match read.

The `no-op` action and listing visibility

There is an action that can be granted called no-op. As might be apparent, no-op is not used for any real action in Boundary; the purpose of this action is for listing visibility. Boundary only shows resources in the output of a list action for which a user has at least one granted action. Thus, without no-op, in order for a resource to be visible in a list action, a different action such as read would have to be granted to a user. This could result in exposing more information than desired, especially in the case of listing scopes and authentication methods so that users can perform initial authentication to Boundary (that is, granting access to u_anon).

By granting the no-op action to users, they can see the resources in the output of a list command without needing other capability grants as well.

Output fields

Grant strings can contain an output_fields field. This allows fine-grained control over visibility of data returned to users.

In many cases, output_fields will not need to be set directly. However, an example in the form of some history helps provide some context as to when this might be useful.

In Boundary 0.2.0, we restricted the set of fields returned for some list calls (those on the scopes and auth-methods collections) to a small set if the user was the anonymous user u_anon. Although default behavior in Boundary was to display all resource fields when listing, because the default was also to allow anonymous access to perform list on scopes and auth methods (in order to discover auth methods and then authenticate to them), returning all configuration information for all scopes and auth methods felt like it was publicly disclosing more information to users than might be desired.

At the same time, this was not an ideal solution for two reasons:

There is no one-size-fits-all security policy, and what we thought were reasonable defaults may not work in all situations
It made the scopes and auth methods listing behavior work differently from any other list action, which is not ideal

As a result, we decided to approach this problem the same way we normally try to within Boundary: set resonable defaults, but give the administrator ultimate control.

The resulting behavior is as follows: output_fields references the field names of the JSON object response, composes just like other parts of the RBAC model, and are action-specific. That is, a grant like:

id=*;type=auth-methods;actions=list,no-op;output_fields=scope_id,name,description

will, if all by itself, result in those three identified output fields applying to list (and no-op) actions for all auth methods in the scope. Thus when performing a list, each item returned will have only those three fields populated. Any other actions (like read or update) are unaffected and will use defaults.

A grant like:

id=*;type=auth-methods;output_fields=id

will, if all by itself, result in any action against auth methods in the scope having only id returned.

However, if both of the above grants are included, since grants are composable the final set of output fields will be id,scope_id,name,description for list (and no-op) actions, and id for all other actions.

If, after the grants are composed for a given request, none of the grants applicable to the resource/action contain output_fields definitions, the defaults are used. These defaults are implemented using internal values for output_fields and vary based on whether the user is the anonymous user:

If the user is the anonymous user, a useful but restricted set of fields is returned. This includes id, scope_id, scope, name, description, and a few more.
If the user is any authenticated user, the full set of fields is returned

To think about it a different way, empty output_fields, after grant composition, is equivalent to using Boundary's default; however the moment that grants start specifying output fields, it is composed from an empty set and thus nothing is contained unless explicitly specified. (An actual empty set is not currently supported, as we don't perform validation on the values given. However, this means setting output_fields=none is functionally equivalent!)

Anonymous user restrictions

Starting in Boundary 0.9.0, there are severe limits placed on the actions allowed to be assigned to the anonymous user u_anon. This is meant to avoid situations where an operator accidentally or mistakenly adds the anonymous user to a role that provides more privileges than might be intended for unauthenticated users.

The set of actions is currently restricted to listing scopes and auth methods and authentication to auth methods (plus no-op actions for listing visibility). If further use cases arise from user feedback, this list can be expanded.

When an anonymous user is denied access, there is no special error message that is returned. It is still possible to assign grants to a role on which the anonymous user is a principal that can never match the anonymous user. In the future this may change, but trying to limit this introduces other restrictions on reasonable administrative workflows, so an acceptable set of tradeoffs would need to be figured out.

Wildcard

Various wildcard possibilities are allowed:

Wildcard ID

When you use only a wildcard for the ID, *, it matches all IDs of the given type. You can use this format with both top-level resource types or none. For example:

id=*;type=host-set;actions=create,read,update,set-hosts

Wildcard type

You can use a wildcard for the type for any non-top-level resources with pinned IDs:

id=hcst_1234567890;type=*;actions=create,read,update

This grant format would allow create, read, and update actions for all types of subordinate resources (in this case host sets and hosts) underneath the host catalog with ID hcst_1234567890.

Wildcard ID and type

If ID and type are both wildcards, the grant is essentially a catch-all that matches any resource of any type within the scope and allows the given actions.

id=*;type=*;actions=read,list

Wildcard ID, type, and actions

Finally, ID, type, and actions can all be wildcards:

id=*;type=*;actions=*

Such a grant is essentially a full administrator grant for a scope.

Templates

A few template possibilities exist, which substitute the given value into the ID field of the grant string at grant evaluation time:

{{.Account.Id}}: The substituted value is the account ID associated with the token used to perform the action. As an example, id={{.Account.Id}};actions=read,change-password" is one of Boundary's default grants to allow users that have authenticated with the Password auth method to change their own password.
- NOTE: Prior to Boundary 0.11.1, {{account.id}} must be used instead. Boundary 0.11.1+ changes this for consistency with other places within Boundary that are gaining templating support, but supports both formats for backwards compatibility.
{{.User.Id}}: The substituted value is the user ID associated with the token used to perform the action.
- NOTE: Prior to Boundary 0.11.1, {{user.id}} must be used instead. Boundary 0.11.1+ changes this for consistency with other places within Boundary that are gaining templating support, but supports both formats for backwards compatibility.