Apache Module mod_auth_form

Available Languages: en

+ + + +

Description:	Form authentication
Status:	Base
Module Identifier:	auth_form_module
Source File:	mod_auth_form.c

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 + usually 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 suitably configured session, + as provided by the mod_session module.

+ +

Directives

AuthFormAuthoritative
AuthFormBody
AuthFormDisableNoStore
AuthFormFakeBasicAuth
AuthFormLocation
AuthFormLoginRequiredLocation
AuthFormLoginSuccessLocation
AuthFormLogoutLocation
AuthFormLogoutLocation
AuthFormMethod
AuthFormMimetype
AuthFormPassword
AuthFormProvider
AuthFormSitePassphrase
AuthFormSize
AuthFormUsername

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.

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 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, while the AuthFormLoginSuccessLocation + directive specifies the URL the user should be redirected to on success.

+ +

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> +

+ +

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.

+ +

When a page protected by mod_auth_form is accessed, and the user is + not logged in, and no AuthFormLoginRequiredLocation + directive is specified as described in the section above, an HTTP_UNAUTHORIZED + status code is returned to the browser in the normal way indicating to the user that + they are not authorised 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 file should contain the login form used to log in, as + per the example below. The key difference in this form is that the HTML + form action is left blank. 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

+ +

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.

+ +

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 reauthentiate, 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, and if authentication + is successful, the original method and body will be retried by Apache, 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 + ... +

+ +

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 nett 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 +

+ +

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.

+ +

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 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.

+ +

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 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.

+ + +

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 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.

+ + +

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 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.

+ +

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 2.3.0 and later

The AuthFormLoginRequiredLocation directive + specifies the URL to redirect to should the user not be authorised to view a page. 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.

+ + +

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 2.3.0 and later

The AuthFormLoginSuccessLocation directive + specifies the URL to redirect to should the user have logged in successfully. 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.

+ + +

AuthFormLogoutLocation Directive

+ + + + + + + + +

Description:	The URI of the page on the server 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 2.3.0 and later

The AuthFormLogoutLocation directive + specifies the URI of a page on the server to redirect to internally should the user + attempt log out.

+ +

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 /logout.html + Session on + ... + + </Location> +

+ +

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

+ + +

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 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.

+ +

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> +

+ +

+ + +

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 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.

+ +

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 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.

+ +

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 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.

+ +

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, + and mod_authnz_ldap.

+ +

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 2.3.0 and later

The AuthFormSitePassphrase directive + specifies a passphrase which, if present in the user session, causes Apache 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.

+ + +

AuthFormSize Directive

+ + + + + + + + +

Description:	The largest size of the form in bytes that will be parsed for the login details
Syntax:	`AuthFormBody size`
Default:	`8192`
Context:	directory
Status:	Base
Module:	mod_auth_form
Compatibility:	Available in Apache 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.

+ + +

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 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.

+ +

Apache Module mod_auth_form

Summary

Warning

Directives

Topics

See also

Basic example

Example login form

Form login handler example

Example login form with location

Warning

Basic inline example

Example inline login form

Example with body preservation

CGI example

Basic logout example

Basic session expiry example

Example

Example

Example

Warning