===========================================================================
 README file for mod_auth_mellon
===========================================================================

mod_auth_mellon is a authentication module for apache. It authenticates
the user against a SAML 2.0 IdP, and and grants access to directories
depending on attributes received from the IdP.


===========================================================================
 Dependencies
===========================================================================

mod_auth_mellon has four dependencies:
 * pkg-config
 * Apache (>=2.0)
 * OpenSSL
 * lasso (>=2.1)

You will also require development headers and tools for all of the
dependencies.

If OpenSSL or lasso are installed in a "strange" directory, then you may
have to specify the directory containing "lasso.pc" and/or "openssl.pc" in
the PKG_CONFIG_PATH environment variable. For example, if openssl is
installed in /usr/local/openssl (with openssl.pc in
/usr/local/openssl/lib/pkgconfig/) and lasso is installed in /opt/lasso
(lasso.pc in /opt/lasso/lib/pkgconfig/), then you can set PKG_CONFIG_PATH
before running configure like this:

PKG_CONFIG_PATH=/usr/local/openssl/lib/pkgconfig:/opt/lasso/lib/pkgconfig
export PKG_CONFIG_PATH


If Apache is installed in a "strange" directory, then you may have to
specify the path to apxs2 using the --with-apxs2=/full/path/to/apxs2
option to configure. If, for example, Apache is installed in /opt/apache,
with apxs2 in /opt/apache/bin, then you run

./configure --with-apxs2=/opt/apache2/bin/apxs2

Note that, depending on your distribution,  apxs2 may be named apxs.


===========================================================================
 Installing mod_auth_mellon
===========================================================================

mod_auth_mellon uses autoconf, and can be installed by running the
following commands:

./configure
make
make install


===========================================================================
 Configuring mod_auth_mellon
===========================================================================

Here we are going to assume that your web servers hostname is
'example.com', and that the directory you are going to protect is
'http://example.com/secret/'. We are also going to assume that you have
configured your web site to use SSL.

You need to edit the configuration file for your web server. Depending on
your distribution, it may be named '/etc/apache/httpd.conf' or something
different.


You need to add a LoadModule directive for mod_auth_mellon. This will
look similar to this:

LoadModule auth_mellon_module /usr/lib/apache2/modules/mod_auth_mellon.so

To find the full path to mod_auth_mellon.so, you may run:

apxs2 -q LIBEXECDIR

This will print the path where Apache stores modules. mod_auth_mellon.so
will be stored in that directory.


After you have added the LoadModule directive, you must add configuration
for mod_auth_mellon. The following is an example configuration:


###########################################################################
# Global configuration for mod_auth_mellon. This configuration is shared by
# every virtual server and location in this instance of apache.
###########################################################################

# MellonCacheSize sets the maximum number of sessions which can be active
# at once. When mod_auth_mellon reaches this limit, it will begin removing
# the least recently used sessions. The server must be restarted before any
# changes to this option takes effect.
# Default: MellonCacheSize 100
MellonCacheSize 100

# MellonCacheEntrySize sets the maximum size for a single session entry in
# bytes. When mod_auth_mellon reaches this limit, it cannot store any more
# data in the session and will return an error. The minimum entry size is
# 65536 bytes, values lower than that will be ignored and the minimum will
# be used.
# Default: MellonCacheEntrySize 196608

# MellonLockFile is the full path to a file used for synchronizing access
# to the session data. The path should only be used by one instance of
# apache at a time. The server must be restarted before any changes to this
# option takes effect.
# Default: MellonLockFile "/var/run/mod_auth_mellon.lock"
MellonLockFile "/var/run/mod_auth_mellon.lock"

# MellonPostDirectory is the full path of a directory where POST requests
# are saved during authentication. This directory must writeable by the
# Apache user. It should not be writeable (or readable) by other users.
# Default: None
# Example: MellonPostDirectory "/var/cache/mod_auth_mellon_postdata"

# MellonPostTTL is the delay in seconds before a saved POST request can
# be flushed.
# Default: MellonPostTTL 900 (15 mn)
MellonPostTTL 900

# MellonPostSize is the maximum size for saved POST requests
# Default: MellonPostSize 1073741824 (1 MB)
MellonPostSize 1073741824

# MellonPostCount is the maximum amount of saved POST requests
# Default: MellonPostCount 100
MellonPostCount 100

###########################################################################
# End of global configuration for mod_auth_mellon.
###########################################################################


# This defines a directory where mod_auth_mellon should do access control.
<Location /secret>

        # These are standard Apache apache configuration directives.
        # See http://httpd.apache.org/docs/2.2/mod/core.html for information
        # about them.
        Require valid-user
        AuthType "Mellon"


        # MellonEnable is used to enable auth_mellon on a location.
        # It has three possible values: "off", "info" and "auth".
        # They have the following meanings:
        #   "off":  mod_auth_mellon will not do anything in this location.
        #           This is the default state.
        #   "info": If the user is authorized to access the resource, then
        #           we will populate the environment with information about
        #           the user. If the user isn't authorized, then we won't
        #           populate the environment, but we won't deny the user
        #           access either.
        #   "auth": We will populate the environment with information about
        #           the user if he is authorized. If he is authenticated
        #           (logged in), but not authorized (according to the
        #           MellonRequire and MellonCond directives, then we will 
        #           return a 403 Forbidden error. If he isn't authenticated
        #           then we will redirect him to the login page of the IdP.
        #
        # Default: MellonEnable "off"
        MellonEnable "auth"

        # MellonDecoder is used to select which decoder mod_auth_mellon
        # will use when decoding attribute values.
        # There are two possible values: "none" and "feide". "none" is the
        # default.
        # They have the following meanings:
        #   "none":  mod_auth_mellon will store the attribute as it is
        #            received from the IdP. This is the default behaviour.
        #   "feide": *DEPRECATED* Feide used to transmit attributes with a
        #            special encoding. That is no longer necessary, and
        #            this decoder should therefore no longer be used.
        # Default: MellonDecoder "none"
        MellonDecoder "none"

        # MellonVariable is used to select the name of the cookie which
        # mod_auth_mellon should use to remember the session id. If you
        # want to have different sites running on the same host, then
        # you will have to choose a different name for the cookie for each
        # site.
        # Default: "cookie"
        MellonVariable "cookie"

        # MellonSecureCookie enforces the HttpOnly and secure flags
        # for the mod_mellon cookie
        # Default: Off
        MellonSecureCookie On

        # MellonCookieDomain allows to specify of the cookie which auth_mellon
        # will set.
        # Default: the domain for the received request (the Host: header if
        # present, of the ServerName of the VirtualHost declaration, or if
        # absent a reverse resolution on the local IP)
        # MellonCookieDomain example.com

        # MellonCookiePath is the path of the cookie which auth_mellon will set.
        # Default: /
        MellonCookiePath /

        # MellonUser selects which attribute we should use for the username.
        # The username is passed on to other apache modules and to the web
        # page the user visits. NAME_ID is an attribute which we set to
        # the id we get from the IdP.
        # Note: If MellonUser refers to a multi-valued attribute, any single
        # value from that attribute may be used. Do not rely on it selecting a
        # specific value.
        # Default: MellonUser "NAME_ID"
        MellonUser "NAME_ID"

        # MellonIdP selects in which attribute we should dump the remote 
        # IdP providerId. This is passed to other apache modules and to 
        # the web pages the user visits.
        # Default: none
        # MellonIdP "IDP"

        # MellonSetEnv configuration directives allows you to map
        # attribute names received from the IdP to names you choose
        # yourself. The syntax is 'MellonSetEnv <local name> <IdP name>'.
        # You can list multiple MellonSetEnv directives.
        # Default. None set.
        MellonSetEnv "e-mail" "mail"

        # MellonSetEnvNoPrefix is identical to MellonSetEnv, except this
        # does not prepend 'MELLON_' to the constructed environment variable.
        # The syntax is 'MellonSetEnvNoPrefix <local name> <IdP name>'.
        # You can list multiple MellonSetEnvNoPrefix directives.
        # Default. None set.
        MellonSetEnvNoPrefix "DISPLAY_NAME" "displayName"

        # If MellonSessionDump is set, then the SAML session will be
        # available in the MELLON_SESSION environment variable
        MellonSessionDump Off
 
        # If MellonSamlResponseDump is set, then the SAML authentication
        # response will be available in the MELLON_SAML_RESPONSE environment 
        # variable
        MellonSamlResponseDump Off
 
        # MellonRequire allows you to limit access to those with specific
        # attributes. The syntax is
        # 'MellonRequire <attribute name> <list of valid values>'.
        # Note that the attribute name is the name we received from the
        # IdP.
        #
        # If you don't list any MellonRequire directives (and any 
        # MellonCond directives, see below), then any user authenticated 
        # by the IdP will have access to this service. If you list several 
        # MellonRequire directives, then all of them will have to match.
        # If you use multiple MellonRequire directive on the same 
        # attribute, the last overrides the previous ones.
        #
        # Default: None set.
        MellonRequire "eduPersonAffiliation" "student" "employee"

        # MellonCond provides the same function as MellonRequire, with
        # extra functionality (MellonRequire is retained for backward
        # compatibility). The syntax is
        # 'MellonCond <attribute name> <value> [<options>]'
        #
        # <value> is an attribute value to match. Unlike with MellonRequire, 
        # multiples values are not allowed.
        #
        # If the [REG] flag is specified (see below), <value> is a regular 
        # expression. The syntax for backslash escape is the same as in
        # Apache's <LocationMatch>'s directives. 
        #
        # Format strings are substituted into <value> prior evaluation. 
        # Here are the supported syntaxes:
        #    %n       With n being a digit between 0 and 9. If [REG,REF] 
        #             flags (see below) were used in an earlier matching 
        #             MellonCond, then regular expression back references
        #             are substituted.
        #    %{num}   Same as %n, with num being a number that may be 
        #             greater than 9.
        #    %{ENV:x} Substitute Apache environment variable x.
        #    %%       Escape substitution to get a literal %.
        #
        # <options> is an optional, comma-separated list of option
        # enclosed with brackets. Here is an example: [NOT,NC]
        # The valid options are:
        #    OR  If this MellonCond evaluated to false, then the
        #        next one will be checked. If it evaluates to true,
        #        then the overall check succeeds.
        #    NOT This MellonCond evaluates to true if the attribute 
        #        does not match the value.
        #    SUB Substring match, evaluates to true if value is
        #        included in attribute.
        #    REG Value to check is a regular expression.
        #    NC  Perform case insensitive match. 
        #    MAP Attempt to search an attribute with name remapped by
        #        MellonSetEnv. Fallback to non remapped name if not
        #        found.
        #    REF Used with REG, track regular expression back references,
        #        So that they can be substituted in an upcoming 
        #        MellonCond directive.
        #        
        # It is allowed to have multiple MellonCond on the same 
        # attribute, and to mix MellonCond and MellonRequire. 
        # Note that this can create tricky situations, since the OR
        # option has effect on a following MellonRequire directive.
        # 
        # Default: none set
        # MellonCond "mail" "@example\.net$" [OR,REG]
        # MellonCond "mail" "@example\.com$" [OR,REG]
        # MellonCond "uid" "superuser"

        # MellonEndpointPath selects which directory mod_auth_mellon
        # should assume contains the SAML 2.0 endpoints. Any request to
        # this directory will be handled by mod_auth_mellon.
        #
        # The path is the full path (from the root of the web server) to
        # the directory. The directory must be a sub-directory of this
        # <Location ...>.
        # Default: MellonEndpointPath "/mellon"
        MellonEndpointPath "/secret/endpoint"

        # MellonDefaultLoginPath is the location where one should be
        # redirected after an IdP-initiated login. Default is "/"
        # Default: MellonDefaultLoginPath "/"
        MellonDefaultLoginPath "/"

        # MellonSessionLength sets the maximum lifetime of a session, in
        # seconds. The actual lifetime may be shorter, depending on the
        # conditions received from the IdP. The default length is 86400
        # seconds, which is one day.
        # Default: MellonSessionLength 86400
        MellonSessionLength 86400

        # MellonNoCookieErrorPage is the full path to a page which
        # mod_auth_mellon will redirect the user to if he returns from the
        # IdP without a cookie with a session id.
        # Note that the user may also get this error if he for some reason
        # loses the cookie between being redirected to the IdP's login page
        # and returning from it.
        # If this option is unset, then mod_auth_mellon will return a
        # 400 Bad Request error if the cookie is missing.
        # Default: unset
        MellonNoCookieErrorPage "https://example.com/no_cookie.html"

        # MellonSPMetadataFile is the full path to the file containing
        # the metadata for this service provider.
        # If mod_auth_mellon was compiled against Lasso version 2.2.2
        # or higher, this option is optional. Otherwise, it is mandatory.
        # Default: None set.
        MellonSPMetadataFile /etc/apache2/mellon/sp-metadata.xml

        # If you choose to autogenerate metadata, this option
        # can be used to control the SP entityId
        # MellonSPentityId "https://www.example.net/foo"
        #
        # If you choose to autogenerate metadata, these options 
        # can be used to fill the <Organization> element. They
        # all follow the syntax "option [lang] value":
        # MellonOrganizationName "random-service"
        # MellonOrganizationDisplayName "en" "Random service"
        # MellonOrganizationDisplayName "fr" "Service quelconque"
        # MellonOrganizationURL "http://www.espci.fr"

        # MellonSPPrivateKeyFile is a .pem file which contains the private
        # key of the service provider. The .pem-file cannot be encrypted
        # with a password. If built with lasso-2.2.2 or higher, the
        # private key only needs to be readable by root, otherwise it has
        # to be readable by the Apache pseudo user.
        # Default: None set.
        MellonSPPrivateKeyFile /etc/apache2/mellon/sp-private-key.pem

        # MellonSPCertFile is a .pem file with the certificate for the
        # service provider. This directive is optional.
        # Default: None set.
        MellonSPCertFile /etc/apache2/mellon/sp-cert.pem

        # MellonIdPMetadataFile is the full path to the file which contains
        # metadata for the IdP you are authenticating against. This
        # directive is required. Multiple IdP metadata can be configured
        # by using multiple MellonIdPMetadataFile directives.
        #
        # If your lasso library is recent enough (higher than 2.3.5),
        # then MellonIdPMetadataFile will accept an XML file containing
        # descriptors for multiple IdP. An optional validating chain can
        # be supplied as a second argument to MellonIdPMetadataFile. If
        # omitted, no metadata validation will take place.
        #
        # Default: None set.
        MellonIdPMetadataFile /etc/apache2/mellon/idp-metadata.xml

        # MellonIdPMetadataGlob is a glob(3) pattern enabled  alternative 
        # to MellonIdPMetadataFile. Like MellonIdPMetadataFile it will
        # accept an optional validating chain if lasso is recent enough.
        #
        # Default: None set.
        #MellonIdPMetadataGlob /etc/apache2/mellon/*-metadata.xml

        # MellonIdpPublicKeyFile is the full path of the public key of the
        # IdP. This parameter is optional if the public key is embedded
        # in the IdP's metadata file, or if a certificate authority is
        # used. This parameter cannot be used if multiple IdP are configured.
        # Default: None set.
        MellonIdPPublicKeyFile /etc/apache2/mellon/idp-public-key.pem

        # MellonIdPCAFile is the full path to the certificate of the
        # certificate authority. This can be used instead of an
        # certificate for the IdP.
        # Default: None set.
        MellonIdPCAFile /etc/apache2/mellon/ca.pem

        # MellonIdPIgnore lists IdP entityId that should not loaded
        # from XML federation metadata files. This is useful if an
        # IdP cause bugs. Multiple entityId may be specified through
        # single MellonIdPIgnore, and multiple MellonIdPIgnore are allowed.
        # Default: None set.
        #MellonIdPIgnore "https://bug.example.net/saml/idp"

        # MellonDiscoveryURL is the URL for IdP discovery service. 
        # This is used for selecting among multiple configured IdP.
        # On initial user authentication, it is redirected to the
        # IdP discovery URL, with the following arguments set:
        #
        #   entityID         SP providerID URL, where our metadata 
        #                    are published.
        #   returnIDParam    Argument that IdP discovery must send back.
        #   return           Return URL the IdP discovery should return to.
        #
        # The IdP discovery must redirect the user to the return URL, 
        # with returnIDParam set to the selected IdP providerID.
        # 
        # The builtin:get-metadata discovery URL is not supported anymore
        # starting with 0.3.1. See MellonProbeDiscoveryTimeout for
        # a replacement.
        #
        # Default: None set.
        MellonDiscoveryURL "http://www.example.net/idp-discovery"

        # MellonProbeDiscoveryTimeout sets the timeout of the
        # IdP probe discovery service, which is available on the
        # probeDisco endoint.
        #
        # This will cause the SP to send HTTP GET requests on the 
        # configured IdP PorviderID URL. Theses URL should be used to
        # publish metadata, though this is not mandatory. If the IdP
        # returns an HTTP status 200, then the IdP is selected. 
        # If the PorviderID URL requires SSL, MellonIdPCAFile is used
        # as a trusted CA bundle.
        #
        # Default: unset, which means the feature is disabled
        # MellonProbeDiscoveryTimeout 1

        # MellonProbeDiscoveryIdP can be used to restrict the 
        # list of IdP queried by the IdP probe discovery service.
        #
        # Default unset, which means that all configured IdP are 
        # queried.
        # MellonProbeDiscoveryIdP http://idp1.example.com/saml/metadata
        # MellonProbeDiscoveryIdP http://idp2.example.net/saml/metadata

        # This option will make the SAML authentication assertion 
        # available in the MELLON_SAML_RESPONSE environment
        # variable. This assertion holds a verifiable signature
        # that can be checked again. Default is Off.
        MellonSamlResponseDump Off

        # This option will make the Lasso session available in 
        # the MELLON_SESSION environment variable. Default is Off.
        MellonSessionDump Off

        # This option will request specific authentication security-level
        # through the AuthnContextClassRef element of the AuthnRequest It will
        # also request enforcement of this level when receiving an
        # authenticating Assertion.
        # If the assertion does not have the required security level, an HTTP
        # Forbidden status code is returned to the browser.
        # MellonAuthnContextClassRef "urn:oasis:names:tc:SAML:2.0:ac:classes:Kerberos"
        # MellonAuthnContextClassRef "urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport"
        # MellonAuthnContextClassRef "urn:oasis:names:tc:SAML:2.0:ac:classes:SoftwarePKI"

        # MellonSubjectConfirmationDataAddressCheck is used to control
        # the checking of client IP address against the address returned by the
        # IdP in Address attribute of the SubjectConfirmationData node. Can be useful if your SP is
        # behind a reverse proxy or any kind of strange network topology making IP address of client
        # different for the IdP and the SP. Default is on.
        # MellonSubjectConfirmationDataAddressCheck On

        # Does not check signature on logout messages exchanges with idp1
        # MellonDoNotVerifyLogoutSignature http://idp1.example.com/saml/metadata

        # Whether to enable replay of POST requests after authentication. When this option is
        # enabled, POST requests that trigger authentication will be saved until the
        # authentication is completed, and then replayed. If this option isn't enabled,
        # the requests will be turned into normal GET requests after authentication.
        #
        # Note that if this option is enabled, you must also
        # set the MellonPostDirectory option in the server configuration.
        #
        # The default is that it is "Off".
        # MellonPostReplay Off

        # Page to redirect to if the IdP sends an error in response to
        # the authentication request.
        #
        # Example:
        #  MellonNoSuccessErrorPage https://sp.example.org/login_failed.html
        #
        # The default is to not redirect, but rather send a
        # 401 Unautorized error.

</Location>


===========================================================================
 Service provider metadata
===========================================================================

The contents of the metadata will depend on your hostname and on what path
you selected with the MellonEndpointPath configuration directive. You can 
supply the metadata using the MellonSPMetadataFile directive, or you
can just let it be autogenerated.

The following is an example of metadata for the example configuration:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<EntityDescriptor
    entityID="examlpe.com"
    xmlns="urn:oasis:names:tc:SAML:2.0:metadata">
  <SPSSODescriptor
      AuthnRequestsSigned="false"
      WantAssertionsSigned="false"
      protocolSupportEnumeration="urn:oasis:names:tc:SAML:2.0:protocol">
    <SingleLogoutService
        Binding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-Redirect"
        Location="https://example.com/secret/endpoint/logout" />
    <NameIDFormat>
      urn:oasis:names:tc:SAML:2.0:nameid-format:transient
    </NameIDFormat>
    <AssertionConsumerService
        index="0"
        isDefault="true"
        Binding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST"
        Location="https://example.com/secret/endpoint/postResponse" />
  </SPSSODescriptor>
</EntityDescriptor>


You should update entityID="example.com" and the two Location attributes.
Note that '/secret/endpoint' in the two Location attributes matches the
path set in MellonEndpointPath.

To use HTTP-Artifact binding instead of the HTTP-POST binding, change
the AssertionConsumerService-element to something like this:

    <AssertionConsumerService
        index="0"
        isDefault="true"
        Binding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-Artifact"
        Location="https://example.com/secret/endpoint/artifactResponse" />

The metadata are published at the 'endpoint/metadata' URL.

===========================================================================
 Using mod_auth_mellon
===========================================================================

After you have set up mod_auth_mellon, you should be able to visit (in our
example) https://example.com/secret/, and be redirected to the IdP's login
page. After logging in you should be returned to
https://example.com/secret/, and get the contents of that page.

When authenticating a user, mod_auth_mellon will set some environment
variables to the attributes it received from the IdP. The name of the
variables will be MELLON_<attribute name>. If you have specified a
different name with the MellonSetEnv or MellonSetEnvNoPrefix configuration
directive, then that name will be used instead. In the case of MellonSetEnv,
the name will still be prefixed by 'MELLON_'.

The value of the attribute will be base64 decoded.

mod_auth_mellon supports multivalued attributes with the following format:
<base64 encoded value>_<base64 encoded value>_<base 64 encoded value>...

If an attribute has multiple values, then they will be stored as
MELLON_<name>_0, MELLON_<name>_1, MELLON_<name>_2, ...

Since mod_auth_mellon doesn't know which attributes may have multiple
values, it will store every attribute at least twice. Once named
MELLON_<name>, and once named <MELLON_<name>_0.

In the case of multivalued attributes MELLON_<name> will contain the first
value.


The following code is a simple php-script which prints out all the
variables:

<?php
header('Content-Type: text/plain');

foreach($_SERVER as $key=>$value) {
  if(substr($key, 0, 7) == 'MELLON_') {
    echo($key . '=' . $value . "\r\n");
  }
}
?>

===========================================================================
 Manual login
===========================================================================

It is possible to manually trigger login operations. This can be done by
accessing "<endpoint path>/login". That endpoint accepts three parameters:

- ReturnTo: A mandatory parameter which contains the URL we should return
  to after login.
- IdP: The entity ID of the IdP we should send a login request to. This
  parameter is optional.
- IsPassive: This parameter can be set to "true" to send a passive
  authentication request to the IdP.

===========================================================================
 Logging out
===========================================================================

mod_auth_mellon supports both IdP initiated and SP initiated logout
through the same endpoint. The endpoint is located at
"<endpoint path>/logout". "<endpoint path>/logoutRequest" is an alias for
this endpoint, provided for compatibility with version 0.0.6 and earlier of
mod_auth_mellon.

To initiate a logout from your web site, you should redirect or link to
"<endpoint path>/logout?ReturnTo=<url to redirect to after logout>". Note
that the ReturnTo parameter is mandatory. For example, if the web site is
located at "https://www.example.com/secret", and the mellon endpoints are
located under "https://www.example.com/secret/endpoint", then the web site
could contain a link element like the following:

<a href=
 "/secret/endpoint/logout?ReturnTo=https://www.example.org/logged_out.html"
 >Log out</a>

This will return the user to "https://www.example.org/logged_out.html"
after the logout operation has completed.

===========================================================================
 Probe IdP discovery 
===========================================================================

mod_auth_mellon has an IdP probe discovery service that sends HTTP GET
to IdP and picks the first that answers. This can be used as a poor
man's failover setup that redirects to your organisation internal IdP. 
Here is a sample configuration:

  MellonEndpointPath "/saml"
  (...)
  MellonDiscoveryUrl "/saml/probeDisco"
  MellonProbeDiscoveryTimeout 1

The SP will sends HTTP GET to each configured IdP providerId URL until
it gets an HTTP 200 response within the 1 second timeout. It will then 
proceed with that IdP.

If you are in a federation, then your IdP login page will need to provide 
an IdP selection feature aimed at users from other institutions (after
such a choice, the user would be redirected to the SP's /saml/login 
endpoint, with ReturnTo and IdP set appropriately). In such a setup, 
you will want to configure external IdP in mod_auth_mellon, but not 
use them for IdP probe discovery. The MellonProbeDiscoveryIdP 
directive can be used to limit the usable IdP for probe discovery:

  MellonEndpointPath "/saml"
  (...)
  MellonDiscoveryUrl "/saml/probeDisco"
  MellonProbeDiscoveryTimeout 1
  MellonProbeDiscoveryIdP "https://idp1.example.net/saml/metadata"
  MellonProbeDiscoveryIdP "https://idp2.example.net/saml/metadata"


===========================================================================
 Replaying POST requests
===========================================================================

By default, POST requests received when the user isn't logged in are turned
into GET requests after authentication. mod_auth_mellon can instead save
the received POST request and replay / repost it after authentication. To
enable this:

1. Create a data directory where mod_auth_mellon can store the saved data:

     mkdir /var/cache/mod_auth_mellon_postdata

2. Set the appropriate permissions on this directory. It needs to be
   accessible for the web server, but nobody else.

     chown www-data /var/cache/mod_auth_mellon_postdata
     chgrp www-data /var/cache/mod_auth_mellon_postdata
     chmod 0700 /var/cache/mod_auth_mellon_postdata

3. Set the MellonPostDirectory option in your server configuration:

     MellonPostDirectory "/var/cache/mod_auth_mellon_postdata"

4. Enable POST replay functionality for the locations you want:

     <Location /secret>
         MellonEnable auth
         [...]
         MellonPostReplay On
     </Location>

After you restart Apache to activate the new configuration, any POST
requests that trigger authentication should now be stored while the
user logs in.

===========================================================================
 Mellon & User Agent Caching behavior
===========================================================================

For each content within Apache Location enabled with "info" or "auth"
mod_auth_mellon sends by default HTTP1.1 Cache-Control header with values
"private, must-revalidate":

- private-value protects content against caching by any proxy servers.
- must-revalidate-value obligates user agent to revalidate maybe locally
  cached or stored content each time on accessing location.

This default behavior ensures that user agent never shows cached static
HTML pages after logout without revalidationg. So that user couldn't be
misleaded about malfunction of logout procedure. Revalidating content after
logout leads to new authentication procedure via mellon.

But mod_auth_mellon will never prohibit specifically any user agent to
cache or store content locally, that have to be revalidated. So that during
the session user agent only revalidates data by server 304-Not-Modified
response and does not have to download content again.

For special content types like images it could make sense to disable
revalidation completely, so that user agent can provide cached and stored
content directly to user. This can be achieved by using other Apache
modules mod_headers and mod_setenvif. E.g. for PNG images:

Using Apache 2.2 configuration options:

  SetEnvIf Request_URI "\.png$" DISABLE_REVALIDATION
  Header always unset Cache-Control env=DISABLE_REVALIDATION

For Apache 2.4 exists shorter notation:

  Header always unset Cache-Control expr=%{CONTENT_TYPE}==image/png

Editing, appanding, overwriting headers is possible in other cases.

===========================================================================
 Contributors
===========================================================================

Thanks to Emmanuel Dreyfus <manu@netbsd.org> for many new features,
including:
- Metadata autogeneration support.
- Support for multiple IdPs.
- IdP discovery service support.
- SOAP logout support.

Benjamin Dauvergne <bdauvergne@entrouvert.com> has contributed many
patches, both with bugfixes and new features:
- Cookie settings, for specifying domain and path of cookie.
- Support for SAML 2.0 authentication contexts.
- Support for running behind a reverse proxy.
- Logout improvements, including support for local logout.