Both Apache and svnserve are capable of granting (or denying) permissions to users. Typically this is done over the entire repository: a user can read the repository (or not), and she can write to the repository (or not). It's also possible, however, to define finer-grained access rules. One set of users may have permission to write to a certain directory in the repository, but not others; another directory might not even be readable by all but a few special people.
Both servers use a common file format to describe these
path-based access rules. In the case of Apache, one needs to
load the mod_authz_svn module and then add
the AuthzSVNAccessFile directive (within
the httpd.conf file) pointing to your own
rules file. (For a full explanation, see
the section called “Per-directory access control”.) If
you're using svnserve, you need to make
the authz-db variable
(within svnserve.conf) point to your
rules file.
Once your server knows where to find your rules file, it's time to define the rules.
The syntax of the file is the same familiar one used
by svnserve.conf and the runtime
configuration files. Lines that start with a hash
(#) are ignored. In its simplest form, each
section names a repository and path within it, as well as the
authenticated usernames are the option names within each
section. The value of each option describes the user's level of
access to the repository path: either
r (read-only) or rw
(read/write). If the user is not mentioned at all, no access is
allowed.
To be more specific: the value of the section names is
either of the form [repos-name:path] or of the
form [path]. If you're using the
SVNParentPath directive, it's important
to specify the repository names in your sections. If you omit
them, a section such as
[/some/dir] will match the path
/some/dir in every
repository. If you're using the SVNPath
directive, however, it's fine to only define paths in your
sections—after all, there's only one repository.
[calc:/branches/calc/bug-142] harry = rw sally = r
In this first example, the user harry has
full read and write access on the
/branches/calc/bug-142 directory in the
calc repository, but the user
sally has read-only access. Any other users
are blocked from accessing this directory.
Of course, permissions are inherited from parent to child directory. That means we can specify a subdirectory with a different access policy for Sally:
[calc:/branches/calc/bug-142] harry = rw sally = r # give sally write access only to the 'testing' subdir [calc:/branches/calc/bug-142/testing] sally = rw
Now Sally can write to the testing
subdirectory of the branch, but can still only read other parts.
Harry, meanwhile, continues to have complete read/write access
to the whole branch.
It's also possible to explicitly deny permission to someone via inheritance rules, by setting the username variable to nothing:
[calc:/branches/calc/bug-142] harry = rw sally = r [calc:/branches/calc/bug-142/secret] harry =
In this example, Harry has read/write access to the
entire bug-142 tree, but has absolutely no
access at all to the secret subdirectory
within it.
The thing to remember is that the most specific path always matches first. The server tries to match the path itself, and then the parent of the path, then the parent of that, and so on. The net effect is that mentioning a specific path in the access file will always override any permissions inherited from parent directories.
By default, nobody has any access to the repository at all.
That means that if you're starting with an empty file, you'll
probably want to give at least read permission to all users at
the root of the repository. You can do this by using the
asterisk variable (*), which means “all
users”:
[/] * = r
This is a common setup; notice that no repository
name is mentioned in the section name. This makes all repositories
world-readable to all users. Once all users have read access to
the repositories, you can give explicit
rw permission to certain users on specific
subdirectories within specific repositories.
The asterisk variable (*) is also worth
special mention because it's the
only pattern that matches an anonymous
user. If you've configured your server block to allow a mixture
of anonymous and authenticated access, all users start out
accessing anonymously. The server looks for a
* value defined for the path being accessed;
if it can't find one, it demands real authentication from
the client.
The access file also allows you to define whole groups of
users, much like the Unix /etc/group
file:
[groups] calc-developers = harry, sally, joe paint-developers = frank, sally, jane everyone = harry, sally, joe, frank, sally, jane
Groups can be granted access control just like users.
Distinguish them with an “at”
(@) prefix:
[calc:/projects/calc] @calc-developers = rw [paint:/projects/paint] jane = r @paint-developers = rw
Another important fact is that
the first matching rule is the one which gets
applied to a user. In the prior example, even though Jane is a
member of the paint-developers group (which has
read/write access), the jane = r rule will be
discovered and matched before the group rule, thus denying Jane
write access.
Groups can also be defined to contain other groups:
[groups] calc-developers = harry, sally, joe paint-developers = frank, sally, jane everyone = @calc-developers, @paint-developers
Subversion 1.5 brings another useful feature to the access
file syntax: username aliases. Some authentication systems
expect and carry relatively short usernames of the sorts we've
been describing here—harry,
sally, joe, and so on. But
other authentication systems—such as those which use LDAP
stores or SSL client certificates—may carry much more
complex usernames. For example, Harry's username in an
LDAP-protected system might be CN=Harold
Hacker,OU=Engineers,DC=red-bean,DC=com. With
usernames like that, the access file can become quite bloated
with long or obscure usernames that are easy to mistype.
Fortunately, username aliases allow you to have to type the
correct complex username only once, in a statement which assigns to
it a more easily digestable alias.
[aliases] harry = CN=Harold Hacker,OU=Engineers,DC=red-bean,DC=com sally = CN=Sally Swatterbug,OU=Engineers,DC=red-bean,DC=com joe = CN=Gerald I. Joseph,OU=Engineers,DC=red-bean,DC=com …
Once you've defined a set of aliases, you can refer to the users elsewhere in the access file via their aliases in all the same places you could have instead used their actual usernames. Simply prepend an ampersand to the alias to distinguish it from a regular username:
[groups] calc-developers = &harry, &sally, &joe paint-developers = &frank, &sally, &jane everyone = @calc-developers, @paint-developers
You might also choose to use aliases if your users' usernames change frequently. Doing so allows you to need to update only the aliases table when these username changes occur, instead of doing global-search-and-replace operations on the whole access file.