DeveloperGuidelinesS3Framework | S3AAA

S3 Authentication, Authorization and Accounting

Authentication is the act of establishing or confirming someone's identity.
Authorization is the concept of allowing access to resources only to those permitted to use them.
Accounting refers to the tracking of user actions - an audit trail.

Overview

AAA functions for S3 are implemented in the modules/s3/s3aaa.py module. This module extends the web2py Auth class as AuthS3 (Authentication), and defines additional classes for role management, access control and audit.

Component	Location	Function
AuthS3	modules/s3/s3aaa.py	Authentication, Login
S3Permission	modules/s3/s3aaa.py	Authorization of Access, ACLs
S3Audit	modules/s3/s3aaa.py	Data access logging, audit trail
S3RoleManager	modules/s3/s3aaa.py	RESTful method to manage roles and ACLs
Admin controllers	controllers/admin.py	User Management, role management

Authentication

Current user

Interactive Login

HTTP Basic Authentication

Roles

Roles are defined in the auth_group table, which is defined by the AuthS3 module (in modules/s3/s3aaa.py).
Each role as an ID, a unique name and an optional description.

Access permissions are granted to roles, while a user gets permissions by assigning roles to him. Role assignment is stored in the auth_membership table, which is defined by the AuthS3 class (in modules/s3/s3aaa.py).

At the start of every request, the IDs of all roles of the currently logged-in user are stored as list in session.s3.roles (in models/00_utils.py. In cases where the user is logged-in during the request (e.g. by HTTP Basic Auth), a refresh of this list is also triggered by the login_bare() method of AuthS3.

Roles can be managed in the S3RoleManager interface (Administration => User Management => Roles).

The following roles are pre-defined in S3 and cannot be changed:

ID	Name	Description
1	Administrator	system administrator
2	Authenticated	all authenticated users
3	Creator	currently unused
4	Editor	data editor

The first registered user gets the Administrator role assigned.
Users with the Administrator role always have all permissions, and may access all pages in Eden. The Administrator may also manage Users, Roles and ACLs.

Users with the Editor role may access all data with all methods, except they can not manage Users, Roles or ACLs.

Every authenticated user gets automatically the Authenticated role assigned. This role assignment cannot be revoked.

Simple Authorization

Simple authorization means, that

• anonymous users have read-only permission
• authenticated users have full access
• the Administrator may additionally access the user management

This is the fallback model wherever there are no ACLs defined.

ACLs

Access Control Lists (ACLs) are bit arrays with each bit representing a permissions to access data with a particular method:

Bit	Value	Permission
auth.permission.CREATE	0x01	may create new records
auth.permission.READ	0x02	may read or list records
auth.permission.UPDATE	0x04	may update existing records
auth.permission.DELETE	0x08	may delete records

ACLs are combinations of these bits (by logical OR), e.g. an ACL with the value 0x06 defines permissions to read and update records, while no permission to add or to delete any records.

ACLs are stored per role and request destination in the s3_permission table, which is defined by the S3Permission class (in modules/s3/s3aaa.py).

For every destination (controller/function/table) two ACLs can be defined to apply depending on whether a user ownes the record or not:

• one ACL for users owning a record (Owner ACL = oacl)
• one ACL for any other user not owning the record (User ACL = uacl).

If a user ownes a record, then the most permissive of the User ACL and the Owner ACL gets applied, otherwise only the User ACL gets applied.

Record Ownership

Tables can implement a record ownership by adding two meta fields:

Field name	Type	Description
created_by	integer (reference auth_user)	ID of the user who has created this record
owned_by	integer (reference auth_group)	ID of the group (role) who own the record

These meta fields are contained in both s3_authorstamp() as well as s3_meta_fields().

A user is considered owner of a record if he has either created the record (user ID == created_by), or he is a member of the owner group (owned_by in user roles).

In tables which do not define either of these meta-fields, ownership rules are not applied (uacl only).

Controller/Table Restriction

ACLs can be defined for controllers, and for particular functions inside controllers.
ACLs can additionally be defined for individual database tables.

The controller ACLs are activated by setting the respective controller to restricted=True in deployment_settings.modules (000_config.py):

    dvi = Storage(
            name_nice = T("Disaster Victim Identification"),
            description = T("Disaster Victim Identification"),

            restricted = True, # Apply controller ACLs

            module_type = 10,
            resources = Storage(
                dvi_recreq = {"importer" : True},
            )
        ),

If restricted is False or not defined, then simple authorization is used for this controller.

The Controller ACL can be defined for all functions in a controller, and additionally for particular functions inside a controller, where the function-specific ACLs override the general controller ACL. That means, you can define a general ACL for the pr controller, and a different one for the pr/person function.

The Controller ACLs are applied to all resources when accessed through this controller/function. If the Controller ACL does not give any permission for the current user (ACL value==auth.permissions.NONE==0x00), then the request is rejected as "Unauthorized". Controllers do not have to implement this check - this is done at a central place (in 00_utils.py).

Once the user has passed that controller permission check (must have at least read permission), and tries to access to a particular table, then the controller checks for table-specific ACLs. This check is to be implemented by the particular controller using s3_has_permission() and s3_accessible_query (except controllers using S3CRUD only, which already contains it).

Note: For consistency reasons, creating or deleting component records in a resource requires additional permission to update the main record, even though the main record is not changed by this operation, e.g. to add an address to a person record, you must also be permitted to update the person record.

If there are specific ACLs defined for the table, then the most restrictive of controller and table ACLs apply (i.e. you cannot allow on the table level what you forbid at the controller level, and vice versa). If there are no specific ACLs defined for this table, then the controller ACLs apply.

Implementation of Access Control

Permission checking is always a two-step process:

1. Check permission to access the controller/function
2. Check permission to access the database table

The first step is done at a central point, in 00_utils.py before the models are loaded. If the ACLs, as defined for the current user, do not specify any permission for the target controller/function, then the request gets rejected before any models are loaded or the controller is entered.

The second step has to be implemented in the respective controller functions. This can be done in two ways:

• the controller uses s3_rest_controller() with S3CRUD, or,
• the controller uses auth.s3_has_permission() and/or auth.s3_accessible_query() to check permissions before exposing any data to the user

s3_has_permission

s3_accessible_query

auth.permission.fail

In case of failure, a well-defined response action must take place:

• in interactive formats:
  • already authenticated users should be informed about the insufficient permissions, and redirected to a (unrestricted) landing page
  • unauthenticated users should be requested to login, and thus forwarded to a login page
• in non-interactive formats:
  • authenticated clients must receive a HTTP 403 (Forbidden) error code to cancel the request properly
  • unauthenticated clients must receive a HTTP 401 (Authorization Required) error in order to trigger an authentication attempt

All this is covered by the auth.permission.fail() method:

authorised = auth.shn_has_permission("delete", db.my_table)
if not authorised:
    auth.permission.fail()

For interactive modes, you can alter the destinations for redirection by setting:

• auth.permission.homepage for redirection when the user is logged-in, but has insufficient privileges (defaults to default/index).
• auth.permission.loginpage for redirection when the user is not logged-in (defaults to default/user/login).

Example: redirect to my/index rather than to default/index in case of insufficient privileges of an authenticated user:

authorised = auth.shn_has_permission("delete", db.my_table)
if not authorised:
    auth.permission.homepage = URL(r=request, c="my", f="index")
    auth.permission.fail()

Data Access Tracking (Audit)

---

DeveloperGuidelinesS3Framework