Autenticación y Autorización

Módulos y Directivas Relacionados

Hay tres tipos de módulos involucrados en los procesos de la autenticación y autorización. Normalmente deberás escoger al menos un módulo de cada grupo.

• Modos de Autenticación (consulte la directiva AuthType )
  • mod_auth_basic
  • mod_auth_digest
• Proveedor de Autenticación (consulte la directiva AuthBasicProvider y AuthDigestProvider)
  • mod_authn_anon
  • mod_authn_dbd
  • mod_authn_dbm
  • mod_authn_file
  • mod_authnz_ldap
  • mod_authn_socache
• Autorización (consulte la directiva Require)
  • mod_authnz_ldap
  • mod_authz_dbd
  • mod_authz_dbm
  • mod_authz_groupfile
  • mod_authz_host
  • mod_authz_owner
  • mod_authz_user

A parte de éstos módulos, también están mod_authn_core y mod_authz_core. Éstos módulos implementan las directivas esenciales que son el centro de todos los módulos de autenticación.

El módulo mod_authnz_ldap es tanto un proveedor de autenticación como de autorización. El módulo mod_authz_host proporciona autorización y control de acceso basado en el nombre del Host, la dirección IP o características de la propia petición, pero no es parte del sistema proveedor de autenticación. Para tener compatibilidad inversa con el mod_access, hay un nuevo modulo llamado mod_access_compat.

También puedes mirar el how-to de Control de Acceso , donde se plantean varias formas del control de acceso al servidor.

Introducción

Si se tiene información en nuestra página web que sea información sensible o pensada para un grupo reducido de usuarios/personas, las técnicas que se describen en este manual, le servirán de ayuda para asegurarse de que las personas que ven esas páginas sean las personas que uno quiere.

Este artículo cubre la parte "estándar" de cómo proteger partes de un sitio web que muchos usarán.

Los Prerequisitos

Las directivas que se usan en este artículo necesitaran ponerse ya sea en el fichero de configuración principal del servidor ( típicamente en la sección <Directory> de httpd.conf ), o en cada uno de los ficheros de configuraciones del propio directorio (los archivos .htaccess).

Si planea usar los ficheros .htaccess , necesitarás tener en la configuración global del servidor, una configuración que permita poner directivas de autenticación en estos ficheros. Esto se hace con la directiva AllowOverride, la cual especifica que directivas, en su caso, pueden ser puestas en cada fichero de configuración por directorio.

Ya que estamos hablando aquí de autenticación, necesitarás una directiva AllowOverride como la siguiente:

AllowOverride AuthConfig

O, si solo se van a poner las directivas directamente en la configuración principal del servidor, deberás tener, claro está, permisos de escritura en el archivo.

Y necesitarás saber un poco de como está estructurado el árbol de directorios de tu servidor, para poder saber donde se encuentran algunos archivos. Esto no debería ser una tarea difícil, aún así intentaremos dejarlo claro llegado el momento de comentar dicho aspecto.

También deberás de asegurarte de que los módulos mod_authn_core y mod_authz_core han sido incorporados, o añadidos a la hora de compilar en tu binario httpd o cargados mediante el archivo de configuración httpd.conf. Estos dos módulos proporcionan directivas básicas y funcionalidades que son críticas para la configuración y uso de autenticación y autorización en el servidor web.

Conseguir que funcione

Aquí está lo básico de cómo proteger con contraseña un directorio en tu servidor.

Primero, necesitarás crear un fichero de contraseña. Dependiendo de que proveedor de autenticación se haya elegido, se hará de una forma u otra. Para empezar, usaremos un fichero de contraseña de tipo texto.

Este fichero deberá estar en un sitio que no se pueda tener acceso desde la web. Esto también implica que nadie pueda descargarse el fichero de contraseñas. Por ejemplo, si tus documentos están guardados fuera de /usr/local/apache/htdocs, querrás poner tu archivo de contraseñas en /usr/local/apache/passwd.

Para crear el fichero de contraseñas, usa la utilidad htpasswd que viene con Apache. Esta herramienta se encuentra en el directorio /bin en donde sea que se ha instalado el Apache. Si ha instalado Apache desde un paquete de terceros, puede ser que se encuentre en su ruta de ejecución.

Para crear el fichero, escribiremos:

htpasswd te preguntará por una contraseña, y después te pedirá que la vuelvas a escribir para confirmarla:

Si htpasswd no está en tu variable de entorno "path" del sistema, por supuesto deberás escribir la ruta absoluta del ejecutable para poder hacer que se ejecute. En una instalación por defecto, está en: /usr/local/apache2/bin/htpasswd

Lo próximo que necesitas, será configurar el servidor para que pida una contraseña y así decirle al servidor que usuarios están autorizados a acceder. Puedes hacer esto ya sea editando el fichero httpd.conf de configuración o usando in fichero .htaccess. Por ejemplo, si quieres proteger el directorio /usr/local/apache/htdocs/secret, puedes usar las siguientes directivas, ya sea en el fichero .htaccess localizado en following directives, either placed in the file /usr/local/apache/htdocs/secret/.htaccess, o en la configuración global del servidor httpd.conf dentro de la sección <Directory "/usr/local/apache/htdocs/secret"> section. como se muesta a continuacion:

<Directory "/usr/local/apache/htdocs/secret">
AuthType Basic
AuthName "Restricted Files"
# (Following line optional)
AuthBasicProvider file
AuthUserFile "/usr/local/apache/passwd/passwords"
Require user rbowen
</Directory>

Let's examine each of those directives individually. The AuthType directive selects that method that is used to authenticate the user. The most common method is Basic, and this is the method implemented by mod_auth_basic. It is important to be aware, however, that Basic authentication sends the password from the client to the server unencrypted. This method should therefore not be used for highly sensitive data, unless accompanied by mod_ssl. Apache supports one other authentication method: AuthType Digest. This method is implemented by mod_auth_digest and was intended to be more secure. This is no longer the case and the connection should be encrypted with mod_ssl instead.

The AuthName directive sets the Realm to be used in the authentication. The realm serves two major functions. First, the client often presents this information to the user as part of the password dialog box. Second, it is used by the client to determine what password to send for a given authenticated area.

So, for example, once a client has authenticated in the "Restricted Files" area, it will automatically retry the same password for any area on the same server that is marked with the "Restricted Files" Realm. Therefore, you can prevent a user from being prompted more than once for a password by letting multiple restricted areas share the same realm. Of course, for security reasons, the client will always need to ask again for the password whenever the hostname of the server changes.

The AuthBasicProvider is, in this case, optional, since file is the default value for this directive. You'll need to use this directive if you are choosing a different source for authentication, such as mod_authn_dbm or mod_authn_dbd.

The AuthUserFile directive sets the path to the password file that we just created with htpasswd. If you have a large number of users, it can be quite slow to search through a plain text file to authenticate the user on each request. Apache also has the ability to store user information in fast database files. The mod_authn_dbm module provides the AuthDBMUserFile directive. These files can be created and manipulated with the dbmmanage and htdbm programs. Many other types of authentication options are available from third party modules in the Apache Modules Database.

Finally, the Require directive provides the authorization part of the process by setting the user that is allowed to access this region of the server. In the next section, we discuss various ways to use the Require directive.

Letting more than one person in

The directives above only let one person (specifically someone with a username of rbowen) into the directory. In most cases, you'll want to let more than one person in. This is where the AuthGroupFile comes in.

If you want to let more than one person in, you'll need to create a group file that associates group names with a list of users in that group. The format of this file is pretty simple, and you can create it with your favorite editor. The contents of the file will look like this:

That's just a list of the members of the group in a long line separated by spaces.

To add a user to your already existing password file, type:

You'll get the same response as before, but it will be appended to the existing file, rather than creating a new file. (It's the -c that makes it create a new password file).

Now, you need to modify your .htaccess file to look like the following:

AuthType Basic
AuthName "By Invitation Only"
# Optional line:
AuthBasicProvider file
AuthUserFile "/usr/local/apache/passwd/passwords"
AuthGroupFile "/usr/local/apache/passwd/groups"
Require group GroupName

Now, anyone that is listed in the group GroupName, and has an entry in the password file, will be let in, if they type the correct password.

There's another way to let multiple users in that is less specific. Rather than creating a group file, you can just use the following directive:

Require valid-user

Using that rather than the Require user rbowen line will allow anyone in that is listed in the password file, and who correctly enters their password. You can even emulate the group behavior here, by just keeping a separate password file for each group. The advantage of this approach is that Apache only has to check one file, rather than two. The disadvantage is that you have to maintain a bunch of password files, and remember to reference the right one in the AuthUserFile directive.

Possible problems

Because of the way that Basic authentication is specified, your username and password must be verified every time you request a document from the server. This is even if you're reloading the same page, and for every image on the page (if they come from a protected directory). As you can imagine, this slows things down a little. The amount that it slows things down is proportional to the size of the password file, because it has to open up that file, and go down the list of users until it gets to your name. And it has to do this every time a page is loaded.

A consequence of this is that there's a practical limit to how many users you can put in one password file. This limit will vary depending on the performance of your particular server machine, but you can expect to see slowdowns once you get above a few hundred entries, and may wish to consider a different authentication method at that time.

Alternate password storage

Because storing passwords in plain text files has the above problems, you may wish to store your passwords somewhere else, such as in a database.

mod_authn_dbm and mod_authn_dbd are two modules which make this possible. Rather than selecting AuthBasicProvider file, instead you can choose dbm or dbd as your storage format.

To select a dbm file rather than a text file, for example:

<Directory "/www/docs/private">
    AuthName "Private"
    AuthType Basic
    AuthBasicProvider dbm
    AuthDBMUserFile "/www/passwords/passwd.dbm"
    Require valid-user
</Directory>

Other options are available. Consult the mod_authn_dbm documentation for more details.

Using multiple providers

With the introduction of the new provider based authentication and authorization architecture, you are no longer locked into a single authentication or authorization method. In fact any number of the providers can be mixed and matched to provide you with exactly the scheme that meets your needs. In the following example, both the file and LDAP based authentication providers are being used.

<Directory "/www/docs/private">
    AuthName "Private"
    AuthType Basic
    AuthBasicProvider file ldap
    AuthUserFile "/usr/local/apache/passwd/passwords"
    AuthLDAPURL ldap://ldaphost/o=yourorg
    Require valid-user
</Directory>

In this example the file provider will attempt to authenticate the user first. If it is unable to authenticate the user, the LDAP provider will be called. This allows the scope of authentication to be broadened if your organization implements more than one type of authentication store. Other authentication and authorization scenarios may include mixing one type of authentication with a different type of authorization. For example, authenticating against a password file yet authorizing against an LDAP directory.

Just as multiple authentication providers can be implemented, multiple authorization methods can also be used. In this example both file group authorization as well as LDAP group authorization is being used.

<Directory "/www/docs/private">
    AuthName "Private"
    AuthType Basic
    AuthBasicProvider file
    AuthUserFile "/usr/local/apache/passwd/passwords"
    AuthLDAPURL ldap://ldaphost/o=yourorg
    AuthGroupFile "/usr/local/apache/passwd/groups"
    Require group GroupName
    Require ldap-group cn=mygroup,o=yourorg
</Directory>

To take authorization a little further, authorization container directives such as <RequireAll> and <RequireAny> allow logic to be applied so that the order in which authorization is handled can be completely controlled through the configuration. See Authorization Containers for an example of how they may be applied.

Beyond just authorization

The way that authorization can be applied is now much more flexible than just a single check against a single data store. Ordering, logic and choosing how authorization will be done is now possible.

Applying logic and ordering

Controlling how and in what order authorization will be applied has been a bit of a mystery in the past. In Apache 2.2 a provider-based authentication mechanism was introduced to decouple the actual authentication process from authorization and supporting functionality. One of the side benefits was that authentication providers could be configured and called in a specific order which didn't depend on the load order of the auth module itself. This same provider based mechanism has been brought forward into authorization as well. What this means is that the Require directive not only specifies which authorization methods should be used, it also specifies the order in which they are called. Multiple authorization methods are called in the same order in which the Require directives appear in the configuration.

With the introduction of authorization container directives such as <RequireAll> and <RequireAny>, the configuration also has control over when the authorization methods are called and what criteria determines when access is granted. See Authorization Containers for an example of how they may be used to express complex authorization logic.

By default all Require directives are handled as though contained within a <RequireAny> container directive. In other words, if any of the specified authorization methods succeed, then authorization is granted.

Using authorization providers for access control

Authentication by username and password is only part of the story. Frequently you want to let people in based on something other than who they are. Something such as where they are coming from.

The authorization providers all, env, host and ip let you allow or deny access based on other host based criteria such as host name or ip address of the machine requesting a document.

The usage of these providers is specified through the Require directive. This directive registers the authorization providers that will be called during the authorization stage of the request processing. For example:

Require ip address
        

where address is an IP address (or a partial IP address) or:

Require host domain_name
        

where domain_name is a fully qualified domain name (or a partial domain name); you may provide multiple addresses or domain names, if desired.

For example, if you have someone spamming your message board, and you want to keep them out, you could do the following:

<RequireAll>
    Require all granted
    Require not ip 10.252.46.165
</RequireAll>

Visitors coming from that address will not be able to see the content covered by this directive. If, instead, you have a machine name, rather than an IP address, you can use that.

<RequireAll>
    Require all granted
    Require not host host.example.com
</RequireAll>

And, if you'd like to block access from an entire domain, you can specify just part of an address or domain name:

<RequireAll>
    Require all granted
    Require not ip 192.168.205
    Require not host phishers.example.com moreidiots.example
    Require not host ke
</RequireAll>

Using <RequireAll> with multiple <Require> directives, each negated with not, will only allow access, if all of negated conditions are true. In other words, access will be blocked, if any of the negated conditions fails.

Access Control backwards compatibility

One of the side effects of adopting a provider based mechanism for authentication is that the previous access control directives Order, Allow, Deny and Satisfy are no longer needed. However to provide backwards compatibility for older configurations, these directives have been moved to the mod_access_compat module.

Authentication Caching

There may be times when authentication puts an unacceptable load on a provider or on your network. This is most likely to affect users of mod_authn_dbd (or third-party/custom providers). To deal with this, HTTPD 2.3/2.4 introduces a new caching provider mod_authn_socache to cache credentials and reduce the load on the origin provider(s).

This may offer a substantial performance boost to some users.

More information

You should also read the documentation for mod_auth_basic and mod_authz_host which contain some more information about how this all works. The directive <AuthnProviderAlias> can also help in simplifying certain authentication configurations.

The various ciphers supported by Apache for authentication data are explained in Password Encryptions.

And you may want to look at the Access Control howto, which discusses a number of related topics.