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Apache > HTTP Server > Documentation > Version 2.5 > Modules

Apache Module mod_auth_form

Available Languages:  en  |  fr 

Description:Form authentication
Status:Base
Module Identifier:auth_form_module
Source File:mod_auth_form.c
Compatibility:Available in Apache 2.3 and later

Summary

Warning

Form authentication depends on the mod_session modules, and these modules make use of HTTP cookies, and as such can fall victim to Cross Site Scripting attacks, or expose potentially private information to clients. Please ensure that the relevant risks have been taken into account before enabling the session functionality on your server.

This module allows the use of an HTML login form to restrict access by looking up users in the given providers. HTML forms require significantly more configuration than the alternatives, however an HTML login form can provide a much friendlier experience for end users.

HTTP basic authentication is provided by mod_auth_basic, and HTTP digest authentication is provided by mod_auth_digest. This module should be combined with at least one authentication module such as mod_authn_file and one authorization module such as mod_authz_user.

Once the user has been successfully authenticated, the user's login details will be stored in a session provided by mod_session.

Directives

Topics

See also

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Basic Configuration

To protect a particular URL with mod_auth_form, you need to decide where you will store your session, and you will need to decide what method you will use to authenticate. In this simple example, the login details will be stored in a session based on mod_session_cookie, and authentication will be attempted against a file using mod_authn_file. If authentication is unsuccessful, the user will be redirected to the form login page.

Basic example

AuthFormProvider file
AuthUserFile conf/passwd
AuthType form
AuthName realm
AuthFormLoginRequiredLocation http://example.com/login.html
Session On
SessionCookieName session path=/
SessionCryptoPassphrase secret

The directive AuthType will enable the mod_auth_form authentication when set to the value form. The directives AuthFormProvider and AuthUserFile specify that usernames and passwords should be checked against the chosen file.

The directives Session, SessionCookieName and SessionCryptoPassphrase create an encrypted session stored within an HTTP cookie on the browser. For more information on the different options for configuring a session, read the documentation for mod_session.

In the simple example above, a URL has been protected by mod_auth_form, but the user has yet to be given an opportunity to enter their username and password. Options for doing so include providing a dedicated standalone login page for this purpose, or for providing the login page inline.

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Standalone Login

The login form can be hosted as a standalone page, or can be provided inline on the same page.

When configuring the login as a standalone page, unsuccessful authentication attempts should be redirected to a login form created by the website for this purpose, using the AuthFormLoginRequiredLocation directive. Typically this login page will contain an HTML form, asking the user to provide their usename and password.

Example login form

<form method="POST" action="/dologin.html">
  Username: <input type="text" name="httpd_username" value="" />
  Password: <input type="password" name="httpd_password" value="" />
  <input type="submit" name="login" value="Login" />
</form>

The part that does the actual login is handled by the form-login-handler. The action of the form should point at this handler, which is configured within Apache httpd as follows:

Form login handler example

<Location /dologin.html>
    SetHandler form-login-handler
    AuthFormLoginRequiredLocation http://example.com/login.html
    AuthFormLoginSuccessLocation http://example.com/success.html
    AuthFormProvider file
    AuthUserFile conf/passwd
    AuthType form
    AuthName realm
    Session On
    SessionCookieName session path=/
    SessionCryptoPassphrase secret
</Location>

The URLs specified by the AuthFormLoginRequiredLocation directive will typically point to a page explaining to the user that their login attempt was unsuccessful, and they should try again. The AuthFormLoginSuccessLocation directive specifies the URL the user should be redirected to upon successful login.

Alternatively, the URL to redirect the user to on success can be embedded within the login form, as in the example below. As a result, the same form-login-handler can be reused for different areas of a website.

Example login form with location

<form method="POST" action="/dologin.html">
  Username: <input type="text" name="httpd_username" value="" />
  Password: <input type="password" name="httpd_password" value="" />
  <input type="submit" name="login" value="Login" />
  <input type="hidden" name="httpd_location" value="http://example.com/success.html" />
</form>
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Inline Login

Warning

A risk exists that under certain circumstances, the login form configured using inline login may be submitted more than once, revealing login credentials to the application running underneath. The administrator must ensure that the underlying application is properly secured to prevent abuse. If in doubt, use the standalone login configuration.

As an alternative to having a dedicated login page for a website, it is possible to configure mod_auth_form to authenticate users inline, without being redirected to another page. This allows the state of the current page to be preserved during the login attempt. This can be useful in a situation where a time limited session is in force, and the session times out in the middle of the user request. The user can be re-authenticated in place, and they can continue where they left off.

If a non-authenticated user attempts to access a page protected by mod_auth_form that isn't configured with a AuthFormLoginRequiredLocation directive, a HTTP_UNAUTHORIZED status code is returned to the browser indicating to the user that they are not authorized to view the page.

To configure inline authentication, the administrator overrides the error document returned by the HTTP_UNAUTHORIZED status code with a custom error document containing the login form, as follows:

Basic inline example

AuthFormProvider file
ErrorDocument 401 /login.shtml
AuthUserFile conf/passwd
AuthType form
AuthName realm
AuthFormLoginRequiredLocation http://example.com/login.html
Session On
SessionCookieName session path=/
SessionCryptoPassphrase secret

The error document page should contain a login form with an empty action property, as per the example below. This has the effect of submitting the form to the original protected URL, without the page having to know what that URL is.

Example inline login form

<form method="POST" action="">
  Username: <input type="text" name="httpd_username" value="" />
  Password: <input type="password" name="httpd_password" value="" />
  <input type="submit" name="login" value="Login" />
</form>

When the end user has filled in their login details, the form will make an HTTP POST request to the original password protected URL. mod_auth_form will intercept this POST request, and if HTML fields are found present for the username and password, the user will be logged in, and the original password protected URL will be returned to the user as a GET request.

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Inline Login with Body Preservation

A limitation of the inline login technique described above is that should an HTML form POST have resulted in the request to authenticate or reauthenticate, the contents of the original form posted by the browser will be lost. Depending on the function of the website, this could present significant inconvenience for the end user.

mod_auth_form addresses this by allowing the method and body of the original request to be embedded in the login form. If authentication is successful, the original method and body will be retried by Apache httpd, preserving the state of the original request.

To enable body preservation, add three additional fields to the login form as per the example below.

Example with body preservation

<form method="POST" action="">
  Username: <input type="text" name="httpd_username" value="" />
  Password: <input type="password" name="httpd_password" value="" />
  <input type="submit" name="login" value="Login" />
  
<input type="hidden" name="httpd_method" value="POST" /> <input type="hidden" name="httpd_mimetype" value="application/x-www-form-urlencoded" /> <input type="hidden" name="httpd_body" value="name1=value1&name2=value2" />
</form>

How the method, mimetype and body of the original request are embedded within the login form will depend on the platform and technology being used within the website.

One option is to use the mod_include module along with the KeptBodySize directive, along with a suitable CGI script to embed the variables in the form.

Another option is to render the login form using a CGI script or other dynamic technology.

CGI example

        AuthFormProvider file
        ErrorDocument 401 /cgi-bin/login.cgi
        ...
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Logging Out

To enable a user to log out of a particular session, configure a page to be handled by the form-logout-handler. Any attempt to access this URL will cause the username and password to be removed from the current session, effectively logging the user out.

By setting the AuthFormLogoutLocation directive, a URL can be specified that the browser will be redirected to on successful logout. This URL might explain to the user that they have been logged out, and give the user the option to log in again.

Basic logout example

SetHandler form-logout-handler
AuthName realm
AuthFormLogoutLocation http://example.com/loggedout.html
Session On
SessionCookieName session path=/
SessionCryptoPassphrase secret

Note that logging a user out does not delete the session; it merely removes the username and password from the session. If this results in an empty session, the net effect will be the removal of that session, but this is not guaranteed. If you want to guarantee the removal of a session, set the SessionMaxAge directive to a small value, like 1 (setting the directive to zero would mean no session age limit).

Basic session expiry example

SetHandler form-logout-handler
AuthFormLogoutLocation http://example.com/loggedout.html
Session On
SessionMaxAge 1
SessionCookieName session path=/
SessionCryptoPassphrase secret
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Usernames and Passwords

Note that form submission involves URLEncoding the form data: in this case the username and password. You should therefore pick usernames and passwords that avoid characters that are URLencoded in form submission, or you may get unexpected results.

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AuthFormAuthoritative Directive

Description:Sets whether authorization and authentication are passed to lower level modules
Syntax:AuthFormAuthoritative On|Off
Default:AuthFormAuthoritative On
Context:directory, .htaccess
Override:AuthConfig
Status:Base
Module:mod_auth_form

Normally, each authorization module listed in AuthFormProvider will attempt to verify the user, and if the user is not found in any provider, access will be denied. Setting the AuthFormAuthoritative directive explicitly to Off allows for both authentication and authorization to be passed on to other non-provider-based modules if there is no userID or rule matching the supplied userID. This should only be necessary when combining mod_auth_form with third-party modules that are not configured with the AuthFormProvider directive. When using such modules, the order of processing is determined in the modules' source code and is not configurable.

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AuthFormBody Directive

Description:The name of a form field carrying the body of the request to attempt on successful login
Syntax:AuthFormBody fieldname
Default:httpd_body
Context:directory
Status:Base
Module:mod_auth_form
Compatibility:Available in Apache HTTP Server 2.3.0 and later

The AuthFormMethod directive specifies the name of an HTML field which, if present, will contain the method of the request to to submit should login be successful.

By populating the form with fields described by AuthFormMethod, AuthFormMimetype and AuthFormBody, a website can retry a request that may have been interrupted by the login screen, or by a session timeout.

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AuthFormDisableNoStore Directive

Description:Disable the CacheControl no-store header on the login page
Syntax:AuthFormDisableNoStore On|Off
Default:AuthFormDisableNoStore Off
Context:directory
Status:Base
Module:mod_auth_form
Compatibility:Available in Apache HTTP Server 2.3.0 and later

The AuthFormDisableNoStore flag disables the sending of a Cache-Control no-store header with the error 401 page returned when the user is not yet logged in. The purpose of the header is to make it difficult for an ecmascript application to attempt to resubmit the login form, and reveal the username and password to the backend application. Disable at your own risk.

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AuthFormFakeBasicAuth Directive

Description:Fake a Basic Authentication header
Syntax:AuthFormFakeBasicAuth On|Off
Default:AuthFormFakeBasicAuth Off
Context:directory
Status:Base
Module:mod_auth_form
Compatibility:Available in Apache HTTP Server 2.3.0 and later

The AuthFormFakeBasicAuth flag determines whether a Basic Authentication header will be added to the request headers. This can be used to expose the username and password to an underlying application, without the underlying application having to be aware of how the login was achieved.

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AuthFormLocation Directive

Description:The name of a form field carrying a URL to redirect to on successful login
Syntax:AuthFormLocation fieldname
Default:httpd_location
Context:directory
Status:Base
Module:mod_auth_form
Compatibility:Available in Apache HTTP Server 2.3.0 and later

The AuthFormLocation directive specifies the name of an HTML field which, if present, will contain a URL to redirect the browser to should login be successful.

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AuthFormLoginRequiredLocation Directive

Description:The URL of the page to be redirected to should login be required
Syntax:AuthFormLoginRequiredLocation url
Default:none
Context:directory
Status:Base
Module:mod_auth_form
Compatibility:Available in Apache HTTP Server 2.3.0 and later

The AuthFormLoginRequiredLocation directive specifies the URL to redirect to should the user not be authorised to view a page. The value is parsed using the ap_expr parser before being sent to the client. By default, if a user is not authorised to view a page, the HTTP response code HTTP_UNAUTHORIZED will be returned with the page specified by the ErrorDocument directive. This directive overrides this default.

Use this directive if you have a dedicated login page to redirect users to.

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AuthFormLoginSuccessLocation Directive

Description:The URL of the page to be redirected to should login be successful
Syntax:AuthFormLoginSuccessLocation url
Default:none
Context:directory
Status:Base
Module:mod_auth_form
Compatibility:Available in Apache HTTP Server 2.3.0 and later

The AuthFormLoginSuccessLocation directive specifies the URL to redirect to should the user have logged in successfully. The value is parsed using the ap_expr parser before being sent to the client. This directive can be overridden if a form field has been defined containing another URL using the AuthFormLocation directive.

Use this directive if you have a dedicated login URL, and you have not embedded the destination page in the login form.

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AuthFormLogoutLocation Directive

Description:The URL to redirect to after a user has logged out
Syntax:AuthFormLogoutLocation uri
Default:none
Context:directory
Status:Base
Module:mod_auth_form
Compatibility:Available in Apache HTTP Server 2.3.0 and later

The AuthFormLogoutLocation directive specifies the URL of a page on the server to redirect to should the user attempt to log out. The value is parsed using the ap_expr parser before being sent to the client.

When a URI is accessed that is served by the handler form-logout-handler, the page specified by this directive will be shown to the end user. For example:

Example

<Location /logout>
    SetHandler form-logout-handler
    AuthFormLogoutLocation http://example.com/loggedout.html
    Session on
    #...
</Location>

An attempt to access the URI /logout/ will result in the user being logged out, and the page /loggedout.html will be displayed. Make sure that the page loggedout.html is not password protected, otherwise the page will not be displayed.

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AuthFormMethod Directive

Description:The name of a form field carrying the method of the request to attempt on successful login
Syntax:AuthFormMethod fieldname
Default:httpd_method
Context:directory
Status:Base
Module:mod_auth_form
Compatibility:Available in Apache HTTP Server 2.3.0 and later

The AuthFormMethod directive specifies the name of an HTML field which, if present, will contain the method of the request to to submit should login be successful.

By populating the form with fields described by AuthFormMethod, AuthFormMimetype and AuthFormBody, a website can retry a request that may have been interrupted by the login screen, or by a session timeout.

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AuthFormMimetype Directive

Description:The name of a form field carrying the mimetype of the body of the request to attempt on successful login
Syntax:AuthFormMimetype fieldname
Default:httpd_mimetype
Context:directory
Status:Base
Module:mod_auth_form
Compatibility:Available in Apache HTTP Server 2.3.0 and later

The AuthFormMethod directive specifies the name of an HTML field which, if present, will contain the mimetype of the request to to submit should login be successful.

By populating the form with fields described by AuthFormMethod, AuthFormMimetype and AuthFormBody, a website can retry a request that may have been interrupted by the login screen, or by a session timeout.

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AuthFormPassword Directive

Description:The name of a form field carrying the login password
Syntax:AuthFormPassword fieldname
Default:httpd_password
Context:directory
Status:Base
Module:mod_auth_form
Compatibility:Available in Apache HTTP Server 2.3.0 and later

The AuthFormPassword directive specifies the name of an HTML field which, if present, will contain the password to be used to log in.

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AuthFormProvider Directive

Description:Sets the authentication provider(s) for this location
Syntax:AuthFormProvider provider-name [provider-name] ...
Default:AuthFormProvider file
Context:directory, .htaccess
Override:AuthConfig
Status:Base
Module:mod_auth_form

The AuthFormProvider directive sets which provider is used to authenticate the users for this location. The default file provider is implemented by the mod_authn_file module. Make sure that the chosen provider module is present in the server.

Example

<Location /secure>
    AuthType form
    AuthName "private area"
    AuthFormProvider  dbm
    AuthDBMType        SDBM
    AuthDBMUserFile    /www/etc/dbmpasswd
    Require            valid-user
    #...
</Location>

Providers are implemented by mod_authn_dbm, mod_authn_file, mod_authn_dbd, mod_authnz_ldap and mod_authn_socache.

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AuthFormSitePassphrase Directive

Description:Bypass authentication checks for high traffic sites
Syntax:AuthFormSitePassphrase secret
Default:none
Context:directory
Status:Base
Module:mod_auth_form
Compatibility:Available in Apache HTTP Server 2.3.0 and later

The AuthFormSitePassphrase directive specifies a passphrase which, if present in the user session, causes Apache httpd to bypass authentication checks for the given URL. It can be used on high traffic websites to reduce the load induced on authentication infrastructure.

The passphrase can be inserted into a user session by adding this directive to the configuration for the form-login-handler. The form-login-handler itself will always run the authentication checks, regardless of whether a passphrase is specified or not.

Warning

If the session is exposed to the user through the use of mod_session_cookie, and the session is not protected with mod_session_crypto, the passphrase is open to potential exposure through a dictionary attack. Regardless of how the session is configured, ensure that this directive is not used within URL spaces where private user data could be exposed, or sensitive transactions can be conducted. Use at own risk.

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AuthFormSize Directive

Description:The largest size of the form in bytes that will be parsed for the login details
Syntax:AuthFormSize size
Default:8192
Context:directory
Status:Base
Module:mod_auth_form
Compatibility:Available in Apache HTTP Server 2.3.0 and later

The AuthFormSize directive specifies the maximum size of the body of the request that will be parsed to find the login form.

If a login request arrives that exceeds this size, the whole request will be aborted with the HTTP response code HTTP_REQUEST_TOO_LARGE.

If you have populated the form with fields described by AuthFormMethod, AuthFormMimetype and AuthFormBody, you probably want to set this field to a similar size as the KeptBodySize directive.

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AuthFormUsername Directive

Description:The name of a form field carrying the login username
Syntax:AuthFormUsername fieldname
Default:httpd_username
Context:directory
Status:Base
Module:mod_auth_form
Compatibility:Available in Apache HTTP Server 2.3.0 and later

The AuthFormUsername directive specifies the name of an HTML field which, if present, will contain the username to be used to log in.

Available Languages:  en  |  fr 

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