1. Alex Willmer
  2. trac-ticketlinks


trac-ticketlinks / trac / wiki / default-pages / TracFineGrainedPermissions

= 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:
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
[trac:source:branches/0.12-stable/tracopt/perm/authz_policy.py 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 [trac:source:branches/0.12-stable/sample-plugins/permissions sample-plugins/permissions] for more examples.

=== !AuthzPolicy === 

 - Install [http://www.voidspace.org.uk/python/configobj.html ConfigObj] (required).
 - Copy authz_policy.py into your plugins directory.
 - Put a [http://swapoff.org/files/authzpolicy.conf 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 [TracIni#trac-section permission_policies] entry in the `[trac]` section
permission_policies = AuthzPolicy, DefaultPermissionPolicy, LegacyAttachmentPolicy
   2. add a new `[authz_policy]` section
authz_file = /some/trac/env/conf/authzpolicy.conf
   3. enable the single file plugin
# 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:

john = WIKI_VIEW
* =
and the default permissions are set like this:
john           WIKI_VIEW
jack           WIKI_VIEW
# anonymous has no WIKI_VIEW

 - 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) === #AuthzSourcePolicy

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  [http://svnbook.red-bean.com/en/1.5/svn.serverconfig.pathbasedauthz.html Path-Based Authorization] section in the Server Configuration chapter of the svn book.

* = r

harry = rw
sally = r

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.

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:

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.

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

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

== Debugging permissions
In trac.ini set:
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.

See also: TracPermissions,
[http://trac-hacks.org/wiki/FineGrainedPageAuthzEditorPlugin TracHacks:FineGrainedPageAuthzEditorPlugin] for a simple editor plugin.