Fine grained permissions

Before Trac 0.11, it was only possible to define fine-grained permissions checks on the repository browser sub-system.

Since 0.11, there's a general mechanism in place that allows custom permission policy plugins to grant or deny any action on any kind of Trac resources, even at the level of specific versions of such resources.

Note that for Trac 0.12, authz_policy has been integrated as an optional module (in tracopt.perm.authz_policy.*), so it's installed by default and can simply be activated via the Plugins panel in the Trac administration module.

Permission Policies

A great diversity of permission policies can be implemented, and Trac comes with a few examples.

Which policies are currently active is determined by a configuration setting in TracIni: e.g.

[trac]
permission_policies = AuthzSourcePolicy, DefaultPermissionPolicy, LegacyAttachmentPolicy

This lists the #AuthzSourcePolicy described below as the first policy, followed by the DefaultPermissionPolicy which checks for the traditional coarse grained style permissions described in TracPermissions, and the LegacyAttachmentPolicy which knows how to use the coarse grained permissions for checking the permissions available on attachments.

Among the possible optional choices, there is #AuthzPolicy, a very generic permission policy, based on an Authz-style system. See ​authz_policy.py for details.

Another popular permission policy #AuthzSourcePolicy, re-implements the pre-0.12 support for checking fine-grained permissions limited to Subversion repositories in terms of the new system.

See also ​sample-plugins/permissions for more examples.

AuthzPolicy

• Install ​ConfigObj (required).
• Copy authz_policy.py into your plugins directory.
• Put a ​authzpolicy.conf file somewhere, preferably on a secured location on the server, not readable for others than the webuser. If the file contains non-ASCII characters, the UTF-8 encoding should be used.
• Update your trac.ini:
  1. modify the permission_policies entry in the [trac] section

     [trac]
     ...
     permission_policies = AuthzPolicy, DefaultPermissionPolicy, LegacyAttachmentPolicy
     

  2. add a new [authz_policy] section

     [authz_policy]
     authz_file = /some/trac/env/conf/authzpolicy.conf
     

  3. enable the single file plugin

     [components]
     ...
     # Trac 0.12
     tracopt.perm.authz_policy.* = enabled
     # for Trac 0.11 use this
     #authz_policy.* = enabled 
     

Note that the order in which permission policies are specified is quite critical, as policies will be examined in the sequence provided.

A policy will return either True, False or None for a given permission check. Only if the return value is None will the next permission policy be consulted. If no policy explicitly grants the permission, the final result will be False (i.e. no permission).

For example, if the authz_file contains:

[wiki:WikiStart@*]
* = WIKI_VIEW

[wiki:PrivatePage@*]
john = WIKI_VIEW
* =

and the default permissions are set like this:

john           WIKI_VIEW
jack           WIKI_VIEW
# anonymous has no WIKI_VIEW

Then:

• All versions of WikiStart will be viewable by everybody (including anonymous)
• PrivatePage will be viewable only by john
• other pages will be viewable only by john and jack

AuthzSourcePolicy (mod_authz_svn-like permission policy)

At the time of this writing, the old fine grained permissions system from Trac 0.11 and before used for restricting access to the repository has been converted to a permission policy component, but from the user point of view, this makes little if no difference.

That kind of fine-grained permission control needs a definition file, which is the one used by Subversion's mod_authz_svn. More information about this file format and about its usage in Subversion is available in the ​Path-Based Authorization section in the Server Configuration chapter of the svn book.

Example:

[/]
* = r

[/branches/calc/bug-142]
harry = rw
sally = r

[/branches/calc/bug-142/secret]
harry =

• / = Everyone has read access by default
• /branches/calc/bug-142 = harry has read/write access, sally read only
• /branches/calc/bug-142/secret = harry has no access, sally has read access (inherited as a sub folder permission)

Trac Configuration

To activate fine grained permissions you must specify the authz_file option in the [trac] section of trac.ini. If this option is set to null or not specified the permissions will not be used.

[trac]
authz_file = /path/to/svnaccessfile

If you want to support the use of the [modulename:/some/path] syntax within the authz_file, add

authz_module_name = modulename

where modulename refers to the same repository indicated by the repository_dir entry in the [trac] section. As an example, if the repository_dir entry in the [trac] section is /srv/active/svn/blahblah, that would yield the following:

[trac]
authz_file = /path/to/svnaccessfile
authz_module_name = blahblah
...
repository_dir = /srv/active/svn/blahblah 

where the svn access file, /path/to/svnaccessfile, contains entries such as [blahblah:/some/path].

Note: Usernames inside the Authz file must be the same as those used inside trac.

As of version 0.12, make sure you have AuthzSourcePolicy included in the permission_policies list in trac.ini, otherwise the authz permissions file will be ignored.

[trac]
permission_policies = AuthzSourcePolicy, DefaultPermissionPolicy, LegacyAttachmentPolicy

Subversion Configuration

The same access file is typically applied to the corresponding Subversion repository using an Apache directive like this:

<Location /repos>
  DAV svn
  SVNParentPath /usr/local/svn

  # our access control policy
  AuthzSVNAccessFile /path/to/svnaccessfile
</Location>

For information about how to restrict access to entire projects in a multiple project environment see ​wiki:TracMultipleProjectsSVNAccess

Debugging permissions

In trac.ini set:

[logging]
log_file = trac.log
log_level = DEBUG
log_type = file

And watch:

tail -n 0 -f log/trac.log | egrep '[perm]|[authz_policy]'

to understand what checks are being performed. See the sourced documentation of the plugin for more info.

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See also: TracPermissions, ​TracHacks:FineGrainedPageAuthzEditorPlugin for a simple editor plugin.