= Trac and mod_wsgi

[https://github.com/GrahamDumpleton/mod_wsgi mod_wsgi] is an Apache module for running WSGI-compatible Python applications directly on top of the Apache webserver. The mod_wsgi adapter is written completely in C and provides very good performance.

[[PageOutline(2-3,Overview,inline)]]

== The `trac.wsgi` script

Trac can be run on top of mod_wsgi with the help of an application script, which is just a Python file saved with a `.wsgi` extension. 

A robust and generic version of this file can be created using the `trac-admin <env> deploy <dir>` command which automatically substitutes the required paths, see TracInstall#cgi-bin. The script should be sufficient for most installations and users not wanting more information can proceed to [#Mappingrequeststothescript configuring Apache].

If you are using Trac with multiple projects, you can specify their common parent directory using the `TRAC_ENV_PARENT_DIR` in trac.wsgi:
{{{#!python
def application(environ, start_request):
    # Add this to config when you have multiple projects                                             
    environ.setdefault('trac.env_parent_dir', '/usr/share/trac/projects')  
    ..
}}}

=== A very basic script
In its simplest form, the script could be:

{{{#!python
import os

os.environ['TRAC_ENV'] = '/usr/local/trac/mysite'
os.environ['PYTHON_EGG_CACHE'] = '/usr/local/trac/mysite/eggs'

import trac.web.main
application = trac.web.main.dispatch_request
}}}

The `TRAC_ENV` variable should naturally be the directory for your Trac environment, and the `PYTHON_EGG_CACHE` should be a directory where Python can temporarily extract Python eggs. If you have several Trac environments in a directory, you can also use `TRAC_ENV_PARENT_DIR` instead of `TRAC_ENV`.

On Windows:
 - If run under the user's session, the Python Egg cache can be found in `%AppData%\Roaming`, for example:
{{{#!python
os.environ['PYTHON_EGG_CACHE'] = r'C:\Users\Administrator\AppData\Roaming\Python-Eggs'
}}}
 - If run under a Window service, you should create a directory for Python Egg cache:
{{{#!python
os.environ['PYTHON_EGG_CACHE'] = r'C:\Trac-Python-Eggs'
}}}

=== A more elaborate script

If you are using multiple `.wsgi` files (for example one per Trac environment) you must ''not'' use `os.environ['TRAC_ENV']` to set the path to the Trac environment. Using this method may lead to Trac delivering the content of another Trac environment, as the variable may be filled with the path of a previously viewed Trac environment. 

To solve this problem, use the following `.wsgi` file instead:
{{{#!python
import os

os.environ['PYTHON_EGG_CACHE'] = '/usr/local/trac/mysite/eggs'

import trac.web.main
def application(environ, start_response):
  environ['trac.env_path'] = '/usr/local/trac/mysite' 
  return trac.web.main.dispatch_request(environ, start_response)
}}}

For clarity, you should give this file a `.wsgi` extension. You should probably put the file in its own directory, since you will expose it to Apache. 

If you have installed Trac and Python eggs in a path different from the standard one, you should add that path by adding the following code at the top of the wsgi script:

{{{#!python
import site
site.addsitedir('/usr/local/trac/lib/python2.4/site-packages')
}}}

Change it according to the path you installed the Trac libs at.

== Mapping requests to the script

After preparing your .wsgi script, add the following to your Apache configuration file, typically `httpd.conf`:

{{{#!apache
WSGIScriptAlias /trac /usr/local/trac/mysite/apache/mysite.wsgi

<Directory /usr/local/trac/mysite/apache>
    WSGIApplicationGroup %{GLOBAL}
    # For Apache 2.2
    <IfModule !mod_authz_core.c>
        Order deny,allow
        Allow from all
    </IfModule>
    # For Apache 2.4
    <IfModule mod_authz_core.c>
        Require all granted
    </IfModule>
</Directory>
}}}

Here, the script is in a subdirectory of the Trac environment.

If you followed the directions [TracInstall#cgi-bin Generating the Trac cgi-bin directory], your Apache configuration file should look like following:

{{{#!apache
WSGIScriptAlias /trac /usr/share/trac/cgi-bin/trac.wsgi

<Directory /usr/share/trac/cgi-bin>
    WSGIApplicationGroup %{GLOBAL}
    # For Apache 2.2
    <IfModule !mod_authz_core.c>
        Order deny,allow
        Allow from all
    </IfModule>
    # For Apache 2.4
    <IfModule mod_authz_core.c>
        Require all granted
    </IfModule>
</Directory>
}}}

In order to let Apache run the script, access to the directory in which the script resides is opened up to all of Apache. Additionally, the `WSGIApplicationGroup` directive ensures that Trac is always run in the first Python interpreter created by mod_wsgi. This is necessary because the Subversion Python bindings, which are used by Trac, don't always work in other sub-interpreters and may cause requests to hang or cause Apache to crash. After adding this configuration, restart Apache, and then it should work.

To test the setup of Apache, mod_wsgi and Python itself (ie. without involving Trac and dependencies), this simple wsgi application can be used to make sure that requests gets served (use as only content in your `.wsgi` script):

{{{#!python
def application(environ, start_response):
        start_response('200 OK',[('Content-type','text/html')])
        return ['<html><body>Hello World!</body></html>']
}}}

For more information about using the mod_wsgi specific directives, see the [http://code.google.com/p/modwsgi/wiki/ mod_wsgi's wiki] and more specifically the [http://code.google.com/p/modwsgi/wiki/IntegrationWithTrac IntegrationWithTrac] page.

== Configuring Authentication

The following sections describe different methods for setting up authentication. See also [http://httpd.apache.org/docs/2.2/howto/auth.html Authentication, Authorization and Access Control] in the Apache guide.

=== Using Basic Authentication

The simplest way to enable authentication with Apache is to create a password file. Use the `htpasswd` program as follows:
{{{#!sh
$ htpasswd -c /somewhere/trac.htpasswd admin
New password: <type password>
Re-type new password: <type password again>
Adding password for user admin
}}}

After the first user, you don't need the "-c" option anymore:
{{{#!sh
$ htpasswd /somewhere/trac.htpasswd john
New password: <type password>
Re-type new password: <type password again>
Adding password for user john
}}}

  ''See the man page for `htpasswd` for full documentation.''

After you've created the users, you can set their permissions using TracPermissions.

Now, you need to enable authentication against the password file in the Apache configuration:
{{{#!apache
<Location "/trac/login">
  AuthType Basic
  AuthName "Trac"
  AuthUserFile /somewhere/trac.htpasswd
  Require valid-user
</Location>
}}}

If you are hosting multiple projects, you can use the same password file for all of them:
{{{#!apache
<LocationMatch "/trac/[^/]+/login">
  AuthType Basic
  AuthName "Trac"
  AuthUserFile /somewhere/trac.htpasswd
  Require valid-user
</LocationMatch>
}}}
Note that neither a file nor a directory named 'login' needs to exist.[[BR]]
See also the [http://httpd.apache.org/docs/2.2/mod/mod_auth_basic.html mod_auth_basic] documentation.

=== Using Digest Authentication

For better security, it is recommended that you either enable SSL or at least use the “digest” authentication scheme instead of “Basic”. 

You have to create your `.htpasswd` file with the `htdigest` command instead of `htpasswd`, as follows:
{{{#!sh
$ htdigest -c /somewhere/trac.htpasswd trac admin
}}}

The "trac" parameter above is the "realm", and will have to be reused in the Apache configuration in the !AuthName directive:

{{{#!apache
<Location "/trac/login">
  AuthType Digest
  AuthName "trac"
  AuthDigestDomain /trac
  AuthUserFile /somewhere/trac.htpasswd
  Require valid-user
</Location>
}}}

For multiple environments, you can use the same `LocationMatch` as described with the previous method.

'''Note: `Location` cannot be used inside .htaccess files, but must instead live within the main httpd.conf file. If you are on a shared server, you therefore will not be able to provide this level of granularity. '''

Don't forget to activate the mod_auth_digest. For example, on a Debian 4.0r1 (etch) system:
{{{#!apache
  LoadModule auth_digest_module /usr/lib/apache2/modules/mod_auth_digest.so
}}}

See also the [http://httpd.apache.org/docs/2.2/mod/mod_auth_digest.html mod_auth_digest] documentation.

=== Using LDAP Authentication 

Configuration for [http://httpd.apache.org/docs/2.2/mod/mod_ldap.html mod_ldap] authentication in Apache is more involved (httpd 2.2.x and OpenLDAP: slapd 2.3.19).

1. You need to load the following modules in Apache httpd.conf:
{{{#!apache
  LoadModule ldap_module modules/mod_ldap.so
  LoadModule authnz_ldap_module modules/mod_authnz_ldap.so
}}}
1. Your httpd.conf also needs to look something like:
{{{#!apache
<Location /trac/>
  # (if you're using it, mod_python specific settings go here)
  Order deny,allow
  Deny from all
  Allow from 192.168.11.0/24
  AuthType Basic
  AuthName "Trac"
  AuthBasicProvider "ldap"
  AuthLDAPURL "ldap://127.0.0.1/dc=example,dc=co,dc=ke?uid?sub?(objectClass=inetOrgPerson)"
  authzldapauthoritative Off
  Require valid-user
</Location>
}}}
1. You can use the LDAP interface as a way to authenticate to a Microsoft Active Directory. Use the following as your LDAP URL:
{{{#!apache
  AuthLDAPURL "ldap://directory.example.com:3268/DC=example,DC=com?sAMAccountName?sub?(objectClass=user)"
}}}
 You will also need to provide an account for Apache to use when checking credentials. As this password will be listed in plaintext in the config, you need to use an account specifically for this task:
{{{#!apache
  AuthLDAPBindDN ldap-auth-user@example.com
  AuthLDAPBindPassword "password"
}}}
 The whole section looks like:
{{{#!apache
<Location /trac/>
  # (if you're using it, mod_python specific settings go here)
  Order deny,allow
  Deny from all
  Allow from 192.168.11.0/24
  AuthType Basic
  AuthName "Trac"
  AuthBasicProvider "ldap"
  AuthLDAPURL "ldap://adserver.company.com:3268/DC=company,DC=com?sAMAccountName?sub?(objectClass=user)"
  AuthLDAPBindDN       ldap-auth-user@company.com
  AuthLDAPBindPassword "the_password"
  authzldapauthoritative Off
  # require valid-user
  Require ldap-group CN=Trac Users,CN=Users,DC=company,DC=com
</Location>
}}}

Note 1: This is the case where the LDAP search will get around the multiple OUs, conecting to the Global Catalog Server portion of AD. Note the port is 3268, not the normal LDAP 389. The GCS is basically a "flattened" tree which allows searching for a user without knowing to which OU they belong.

Note 2: You can also require the user be a member of a certain LDAP group, instead of just having a valid login:
{{{#!apache
  Require ldap-group CN=Trac Users,CN=Users,DC=example,DC=com
}}}

See also:
 - [http://httpd.apache.org/docs/2.2/mod/mod_authnz_ldap.html mod_authnz_ldap], documentation for mod_authnz_ldap.   
 - [http://httpd.apache.org/docs/2.2/mod/mod_ldap.html mod_ldap], documentation for mod_ldap, which provides connection pooling and a shared cache.
 - [http://trac-hacks.org/wiki/LdapPlugin TracHacks:LdapPlugin] for storing TracPermissions in LDAP.

=== Using SSPI Authentication

If you are using Apache on Windows, you can use mod_auth_sspi to provide single-sign-on. Download the module from the !SourceForge [http://sourceforge.net/projects/mod-auth-sspi/ mod-auth-sspi project] and then add the following to your !VirtualHost:
{{{#!apache
<Location /trac/login>
  AuthType SSPI
  AuthName "Trac Login"
  SSPIAuth On
  SSPIAuthoritative On
  SSPIDomain MyLocalDomain
  SSPIOfferBasic On
  SSPIOmitDomain Off
  SSPIBasicPreferred On
  Require valid-user
</Location>
}}}

Using the above, usernames in Trac will be of the form `DOMAIN\username`, so you may have to re-add permissions and such. If you do not want the domain to be part of the username, set `SSPIOmitDomain On` instead.

Some common problems with SSPI authentication: [trac:#1055], [trac:#1168] and [trac:#3338].

See also [trac:TracOnWindows/Advanced].

=== Using CA !SiteMinder Authentication
Setup CA !SiteMinder to protect your Trac login URL (e.g. /trac/login).  Then modify the trac.wsgi script generated using `trac-admin <env> deploy <dir>` to add the following lines, which extract the HTTP_SM_USER variable and set it to REMOTE_USER:

{{{#!python
def application(environ, start_request): 
    # Set authenticated username on CA SiteMinder to REMOTE_USER variable 
    # strip() is used to remove any spaces on the end of the string
    if 'HTTP_SM_USER' in environ: 
        environ['REMOTE_USER'] = environ['HTTP_SM_USER'].strip()
    ...
}}}

Note:  you do not need any Apache "Location" directives.

=== Using Apache authentication with the Account Manager plugin's Login form ===

To begin with, see the basic instructions for using the Account Manager plugin's [http://trac-hacks.org/wiki/AccountManagerPlugin/Modules#LoginModule Login module] and its [http://trac-hacks.org/wiki/AccountManagerPlugin/AuthStores#HttpAuthStore HttpAuthStore authentication module].

'''Note:''' If is difficult to get !HttpAuthStore to work with WSGI when using any Account Manager version prior to acct_mgr-0.4. Upgrading is recommended.

Here is an example (from the !HttpAuthStore link) using acct_mgr-0.4 for hosting a single project:
{{{#!ini
[components]
; be sure to enable the component
acct_mgr.http.HttpAuthStore = enabled

[account-manager]
; configure the plugin to use a page that is secured with http authentication
authentication_url = /authFile
password_store = HttpAuthStore
}}}
This will generally be matched with an Apache config like:
{{{#!apache
<Location /authFile>
   …HTTP authentication configuration…
   Require valid-user
</Location>
}}}
Note that '''authFile''' need not exist (unless you are using Account Manager older than 0.4). See the !HttpAuthStore link above for examples where multiple Trac projects are hosted on a server.

=== Example: Apache/mod_wsgi with Basic Authentication, Trac being at the root of a virtual host

Per the mod_wsgi documentation linked to above, here is an example Apache configuration that:
 - serves the Trac instance from a virtualhost subdomain
 - uses Apache basic authentication for Trac authentication.

If you want your Trac to be served from e.g. !http://trac.my-proj.my-site.org, then from the folder e.g. `/home/trac-for-my-proj`, if you used the command `trac-admin the-env initenv` to create a folder `the-env`, and you used `trac-admin the-env deploy the-deploy` to create a folder `the-deploy`, then first:

Create the htpasswd file:
{{{#!sh
cd /home/trac-for-my-proj/the-env
htpasswd -c htpasswd firstuser
### and add more users to it as needed:
htpasswd htpasswd seconduser
}}}
Keep the file above your document root for security reasons.

Create this file e.g. (ubuntu) `/etc/apache2/sites-enabled/trac.my-proj.my-site.org.conf` with the following content:

{{{#!apache
<Directory /home/trac-for-my-proj/the-deploy/cgi-bin/trac.wsgi>
  WSGIApplicationGroup %{GLOBAL}
  Order deny,allow
  Allow from all
</Directory>

<VirtualHost *:80>
  ServerName trac.my-proj.my-site.org
  DocumentRoot /home/trac-for-my-proj/the-env/htdocs/
  WSGIScriptAlias / /home/trac-for-my-proj/the-deploy/cgi-bin/trac.wsgi
  <Location '/'>
    AuthType Basic
    AuthName "Trac"
    AuthUserFile /home/trac-for-my-proj/the-env/htpasswd
    Require valid-user
  </Location>
</VirtualHost>

}}}

Note: for subdomains to work you would probably also need to alter `/etc/hosts` and add A-Records to your host's DNS.

== Troubleshooting

=== Use a recent version

Please use either version 1.6, 2.4 or later of `mod_wsgi`. Versions prior to 2.4 in the 2.X branch have problems with some Apache configurations that use WSGI file wrapper extension. This extension is used in Trac to serve up attachments and static media files such as style sheets. If you are affected by this problem, attachments will appear to be empty and formatting of HTML pages will appear not to work due to style sheet files not loading properly. Another frequent symptom is that binary attachment downloads are truncated. See mod_wsgi tickets [http://code.google.com/p/modwsgi/issues/detail?id=100 #100] and [http://code.google.com/p/modwsgi/issues/detail?id=132 #132].

''Note: using mod_wsgi 2.5 and Python 2.6.1 gave an Internal Server Error on my system (Apache 2.2.11 and Trac 0.11.2.1). Upgrading to Python 2.6.2 (as suggested [http://www.mail-archive.com/modwsgi@googlegroups.com/msg01917.html here]) solved this for me[[BR]]-- Graham Shanks''

If you plan to use `mod_wsgi` in embedded mode on Windows or with the MPM worker on Linux, then you will need version 3.4 or greater. See [trac:#10675] for details.

=== Getting Trac to work nicely with SSPI and 'Require Group'

If you have set Trac up on Apache, Win32 and configured SSPI, but added a 'Require group' option to your apache configuration, then the SSPIOmitDomain option is probably not working. If it is not working, your usernames in Trac probably look like 'DOMAIN\user' rather than 'user'.

This WSGI script 'fixes' that:
{{{#!python
import os
import trac.web.main

os.environ['TRAC_ENV'] = '/usr/local/trac/mysite'
os.environ['PYTHON_EGG_CACHE'] = '/usr/local/trac/mysite/eggs'

def application(environ, start_response):
    if "\\" in environ['REMOTE_USER']:
        environ['REMOTE_USER'] = environ['REMOTE_USER'].split("\\", 1)[1]
    return trac.web.main.dispatch_request(environ, start_response)
}}}

=== Trac with PostgreSQL

When using the mod_wsgi adapter with multiple Trac instances and PostgreSQL (or MySQL?) as the database, the server ''may'' create a lot of open database connections and thus PostgreSQL processes.

A somewhat brutal workaround is to disable connection pooling in Trac. This is done by setting `poolable = False` in `trac.db.postgres_backend` on the `PostgreSQLConnection` class.

But it is not necessary to edit the source of Trac. The following lines in `trac.wsgi` will also work:

{{{#!python
import trac.db.postgres_backend
trac.db.postgres_backend.PostgreSQLConnection.poolable = False
}}}

or

{{{#!python
import trac.db.mysql_backend
trac.db.mysql_backend.MySQLConnection.poolable = False
}}}

Now Trac drops the connection after serving a page and the connection count on the database will be kept low.

//This is not a recommended approach though. See also the notes at the bottom of the [http://code.google.com/p/modwsgi/wiki/IntegrationWithTrac mod_wsgi's IntegrationWithTrac] wiki page.//

=== Other resources

For more troubleshooting tips, see also the [TracModPython#Troubleshooting mod_python troubleshooting] section, as most Apache-related issues are quite similar, plus discussion of potential [http://code.google.com/p/modwsgi/wiki/ApplicationIssues application issues] when using mod_wsgi. The wsgi page also has a [http://code.google.com/p/modwsgi/wiki/IntegrationWithTrac Integration With Trac] document.

----
See also: TracGuide, TracInstall, [wiki:TracFastCgi FastCGI], [wiki:TracModPython ModPython], [trac:TracNginxRecipe TracNginxRecipe]