Apache Module mod_auth_form

Summary

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 bymod_auth_basic, and HTTP digest authentication is provided bymod_auth_digest. This module should be combined with at least one authentication module such asmod_authn_file and one authorization module such asmod_authz_user.

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

Topics

• Basic Configuration
• Standalone Login
• Inline Login
• Inline Login with Body Preservation
• Logging Out
• Usernames and Passwords

Directives

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

Bugfix checklist

• httpd changelog
• Known issues
• Report a bug

See also

• mod_session
• AuthName
• AuthType
• Require
• Authentication howto
• Comments

Basic Configuration

To protect a particular URL withmod_auth_form, you need to decide where you will store yoursession, 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 onmod_session_cookie, and authentication will be attempted against a file usingmod_authn_file. If authentication is unsuccessful, the user will be redirected to the form login page.

<Location "/admin">    AuthFormProvider file    AuthUserFile "conf/passwd"    AuthType form    AuthName "/admin"    AuthFormLoginRequiredLocation "http://example.com/login.html"    Session On    SessionCookieName session path=/    Require valid-user</Location>

The directiveAuthType will enable themod_auth_form authentication when set to the valueform. The directivesAuthFormProvider andAuthUserFile specify that usernames and passwords should be checked against the chosen file.

The directivesSession andSessionCookieName session stored within an HTTP cookie on the browser. For more information on the different options for configuring a session, read the documentation formod_session.

You can optionally add aSessionCryptoPassphrase to create an encrypted session cookie. This required the additional modulemod_session_crypto be loaded.

In the simple example above, a URL has been protected bymod_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 theAuthFormLoginRequiredLocation directive. Typically this login page will contain an HTML form, asking the user to provide their usename and password.

<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 theform-login-handler. The action of the form should point at this handler, which is configured within Apache httpd as follows:

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

The URLs specified by theAuthFormLoginRequiredLocation directive will typically point to a page explaining to the user that their login attempt was unsuccessful, and they should try again. TheAuthFormLoginSuccessLocation 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 sameform-login-handler can be reused for different areas of a website.

<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

As an alternative to having a dedicated login page for a website, it is possible to configuremod_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 bymod_auth_form that isn't configured with aAuthFormLoginRequiredLocation directive, aHTTP_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 theHTTP_UNAUTHORIZED status code with a custom error document containing the login form, as follows:

AuthFormProvider fileErrorDocument 401 "/login.shtml"AuthUserFile "conf/passwd"AuthType formAuthName realmSession OnSessionCookieName session path=/

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.

<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.

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.

<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 themod_include module along with theKeptBodySize 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.

AuthFormProvider fileErrorDocument 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 theform-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 theAuthFormLogoutLocation 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.

SetHandler form-logout-handlerAuthName realmAuthFormLogoutLocation "http://example.com/loggedout.html"Session OnSessionCookieName session path=/

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 theSessionMaxAge directive to a small value, like 1 (setting the directive to zero would mean no session age limit).

SetHandler form-logout-handlerAuthFormLogoutLocation "http://example.com/loggedout.html"Session OnSessionMaxAge 1SessionCookieName session path=/

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.

AuthFormAuthoritativeDirective

Normally, each authorization module listed inAuthFormProvider will attempt to verify the user, and if the user is not found in any provider, access will be denied. Setting theAuthFormAuthoritative directive explicitly toOff allows for both authentication and authorization to be passed on to other non-provider-based modules if there isno userID orrule matching the supplied userID. This should only be necessary when combiningmod_auth_form with third-party modules that are not configured with theAuthFormProvider directive. When using such modules, the order of processing is determined in the modules' source code and is not configurable.

AuthFormBodyDirective

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

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

AuthFormDisableNoStoreDirective

TheAuthFormDisableNoStore flag disables the sending of aCache-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 anecmascript application to attempt to resubmit the login form, and reveal the username and password to the backend application. Disable at your own risk.

AuthFormFakeBasicAuthDirective

TheAuthFormFakeBasicAuth flag determines whether aBasic 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.

AuthFormLocationDirective

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

AuthFormLoginRequiredLocationDirective

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

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

AuthFormLoginSuccessLocationDirective

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

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

AuthFormLogoutLocationDirective

TheAuthFormLogoutLocation 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 theap_expr parser before being sent to the client.

When a URI is accessed that is served by the handlerform-logout-handler, the page specified by this directive will be shown to the end user. For 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 pageloggedout.html is not password protected, otherwise the page will not be displayed.

AuthFormMethodDirective

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

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

AuthFormMimetypeDirective

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

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

AuthFormPasswordDirective

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

AuthFormProviderDirective

TheAuthFormProvider directive sets which provider is used to authenticate the users for this location. The defaultfile provider is implemented by themod_authn_file module. Make sure that the chosen provider module is present in the server.

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

Providers are implemented bymod_authn_dbm,mod_authn_file,mod_authn_dbd,mod_authnz_ldap andmod_authn_socache.

AuthFormSitePassphraseDirective

TheAuthFormSitePassphrase 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 theform-login-handler. Theform-login-handler itself will always run the authentication checks, regardless of whether a passphrase is specified or not.

AuthFormSizeDirective

TheAuthFormSize 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 codeHTTP_REQUEST_TOO_LARGE.

If you have populated the form with fields described byAuthFormMethod,AuthFormMimetype andAuthFormBody, you probably want to set this field to a similar size as theKeptBodySize directive.

AuthFormUsernameDirective

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