Difference between revisions of "External services security"

Jump to: navigation, search
(Application embedding)
Line 192: Line 192:
it is not necessary to use WS layers defined in /webservices/xxx/, the same infrastructure may be used in all ajax scripts that do not have access to browser cookies.
it is not necessary to use WS layers defined in /webservices/xxx/, the same infrastructure may be used in all ajax scripts that do not have access to browser cookies.
It would not be practical to list all approved users, instead we can use capabilities
for access restrictions. The required capability is given in the service definition table.
==RSS and other feeds==
==RSS and other feeds==

Revision as of 22:48, 7 October 2009

Moodle 2.0

Descriptions of security framework for web services, also used for RSS feeds, embedded application and similar parts that can not use normal HTTP cookies.


Current solutions:

  • user keys for gradebook import and export - see require_user_key_login() and db table user_private_key
  • open RSS feeds - no security at all
  • chat_sid tokens - generated separately for each user in each chat
  • calendar export - hash from user name, password and salt
  • hacky cookie emulation in visual gradebook plugin


Different uses

The external API may be used from different places:

  1. directly from PHP - no authentication, current user session is used ($USER, $SESSION)
  2. simple web service layer - easy to use and setup WS layer designed for interaction with enterprise systems (each having own single purpose user account), the protocol is stateless, username and password is sent with each request; security is enforced on multiple levels
  3. full WS layer with token authentication - it is more flexible and enables normal users to use some restricted parts of the WS APIs, performance might be significantly improved by emulation of sessions
  4. when embedding external applications - external application receives unique token which is used instead of normal browser session cookie, the session is linked to the current user session in browser, the token is automatically invalidated after logout
  5. RSS feeds, iCals, etc. - token login, no permanent session

API layers

Three layers:

  1. external server interface (SOAP, REST, RSS, etc.) - deals with tokens, emulates user session, parameter processing
  2. public PHP API - functions usable directly from PHP, list generated from inline PHP docs, need to verify all parameters and access control, may access $USER, should not manipulate $SESSION directly, must not read $_POST or $_GET
  3. low level internal API - as fast as possible, basic param validation, no access control, must not touch $USER, $SESSION, $_GET or $_POST, must not use has_capability() or require_login()!

Context restrictions

Context restriction of token validity should be effective against security problems in external applications interacting with Moodle. Some external applications do not have any access to http cookies, solution is to create temporary tokens. Context restrictions would allow us to grant external access to individual activities, courses ,etc..



This simplest case of using the external API. The calling call has to make sure the current $USER and $SESSION is valid. Optionally the caller may set up the context restriction manually. This should be the easiest way to start with Moodle modifications and integration with other PHP software.

Simplified web services

This type of web service is using simple username+password authentication (in future could be username+certificate). The communication integrity/privacy can be protected using https. Each external application is using own user account. These user accounts can not be used for normal login into moodle vie web interface.

This type of WS is intended primarily for integration with student information systems or other enterprise software.

webservice auth plugin

It is recommended to create separate user for each external application. The benefit of this auth type is that it can not be used for normal log-in from the web interface. User preferences may be later used for storage of extra data such as public certificates.

WS entry point

Separate php file /webservice/xxx/simpleserver.php

external_services_users table

Specifies which user may use each external service. The restrictedusers flag is ignored in this type of WS, each user must have entry in this table in order to use service functions.

Field Type Default Description
id int(10) auto-incrementing
externalserviceid int(10) foreign key, reference external_services.id
userid int(10) foreign key, reference user.id
iprestriction varchar(255) restrict access to some ips or subnets only
validuntil int(10) invalidate after
timecreated int(10) time when this record added

Steps needed to configure simple web services access

  1. enable simple web services - global switch affecting all simple web services (admin UI)
  2. create new service in some local plug-ip (add code into /local/yourplugin/db/services.php)
  3. add new user, set auth plugin to webservice (normal add user UI)
  4. enable web service layer plugin (admin UI)
  5. add user into list of users that are allowed to use specific external services (admin UI)
  6. set up user permissions needed in function implementations
  7. set up permission to use specific web services (optional, services do not need to specify required capability)

General web services

More flexible than the WS with simplified authentication and setup. The performance may be significantly improved by emulation of sessions. The authentication is based on security tokens (user, context and purpose specific) that are generated in normal Moodle interface and then used in other external applications that are using our web services. This allows us to give only partial access to some parts of WS api, external applications and services do not need to be fully trusted.

The main drawback is that the complex configuration does not encourage admins to keep everything secured.


Stores permanent tokens for cookieless access, script runs without real session. (Later we will might have to add emulated session for performance reasons.)

Field Type Default Description
id int(10) auto-incrementing
userid int(10) foreign key, references user.id
token varchar(128) private access key value
tokentype int(3) type of token: 0=permanent, no session; 1=linked to current browser session via sid; 2=permanent, with emulated session
sid varchar(128) NULL links to browser or emulated session
restrictioncontextid int(10) security restriction, key usable only in this context, references context.id
externalserviceid int(10) foreign key, references external_services.id
itemid int(10) 0 Service specific item id
iprestriction varchar(255) null IP address restriction, list of allowed addresses
validuntil int(10) null timestampt - valid until date
timecreated int(10) time when key created
lastaccess int(10) time when key last used for access

Steps needed to configure general web services access

  1. enable general web services - global switch affecting all general web services (admin UI)
  2. enable web service layer plugins (admin UI)
  3. setup user permission which allows them to create tokens in some specific context for some specific purpose (roles UI)
  4. set up user permissions needed in function implementations
  5. set up permission to use specific web services (optional, services do not need to specify required capability)
  6. each user must create permanent token in specific context for specific purpose (user UI)
  7. user must copy/past this token to external application

Application embedding

Similar to general WS, the token is linked to current session - when user logs out, the external token is immediately invalidated. The administration is much easier and the tokens are usually created automatically.

The external applications maybe be embedded into browser or they can be launched as separate programs (ex.: Java Web Start, Flex, external media players, etc.)

it is not necessary to use WS layers defined in /webservices/xxx/, the same infrastructure may be used in all ajax scripts that do not have access to browser cookies.

RSS and other feeds

Examples: gradebook exports, private RSS feeds

See also