Invocation modes

The invocation modes for FastCGI authorizers supported by this module are distinguished by two characteristics, type and auth mechanism.

Type is simply authn for authentication, authz for authorization, or authnz for combined authentication and authorization.

Auth mechanism refers to the Apache httpd configuration mechanisms and processing phases, and can be AuthBasicProvider, Require, or check_user_id. The first two of these correspond to the directives used to enable participation in the appropriate processing phase.

Descriptions of each mode:

Type authn, mechanism AuthBasicProvider

In this mode, FCGI_ROLE is set to AUTHORIZER and FCGI_APACHE_ROLE is set to AUTHENTICATOR. The application must be defined as provider type authn using AuthnzFcgiDefineProvider and enabled with AuthBasicProvider. When invoked, the application is expected to authenticate the client using the provided user id and password. Example application:

#!/usr/bin/perl
use FCGI;
my $request = FCGI::Request();
while ($request->Accept() >= 0) {
    die if $ENV{'FCGI_APACHE_ROLE'} ne "AUTHENTICATOR";
    die if $ENV{'FCGI_ROLE'}        ne "AUTHORIZER";
    die if !$ENV{'REMOTE_PASSWD'};
    die if !$ENV{'REMOTE_USER'};

    print STDERR "This text is written to the web server error log.\n";

    if ( ($ENV{'REMOTE_USER' } eq "foo" || $ENV{'REMOTE_USER'} eq "foo1") &&
        $ENV{'REMOTE_PASSWD'} eq "bar" ) {
        print "Status: 200\n";
        print "Variable-AUTHN_1: authn_01\n";
        print "Variable-AUTHN_2: authn_02\n";
        print "\n";
    }
    else {
        print "Status: 401\n\n";
    }
}

Example configuration:

AuthnzFcgiDefineProvider authn FooAuthn fcgi://localhost:10102/
<Location "/protected/">
  AuthType Basic
  AuthName "Restricted"
  AuthBasicProvider FooAuthn
  Require ...
</Location>

Type authz, mechanism Require

In this mode, FCGI_ROLE is set to AUTHORIZER and FCGI_APACHE_ROLE is set to AUTHORIZER. The application must be defined as provider type authz using AuthnzFcgiDefineProvider. When invoked, the application is expected to authorize the client using the provided user id and other request data. Example application:

#!/usr/bin/perl
use FCGI;
my $request = FCGI::Request();
while ($request->Accept() >= 0) {
    die if $ENV{'FCGI_APACHE_ROLE'} ne "AUTHORIZER";
    die if $ENV{'FCGI_ROLE'}        ne "AUTHORIZER";
    die if $ENV{'REMOTE_PASSWD'};

    print STDERR "This text is written to the web server error log.\n";

    if ($ENV{'REMOTE_USER'} eq "foo1") {
        print "Status: 200\n";
        print "Variable-AUTHZ_1: authz_01\n";
        print "Variable-AUTHZ_2: authz_02\n";
        print "\n";
    }
    else {
        print "Status: 403\n\n";
    }
}

Example configuration:

AuthnzFcgiDefineProvider authz FooAuthz fcgi://localhost:10103/
<Location "/protected/">
  AuthType ...
  AuthName ...
  AuthBasicProvider ...
  Require FooAuthz
</Location>

Type authnz, mechanism AuthBasicProvider + Require

In this mode, which supports the web server-agnostic FastCGI AUTHORIZER protocol, FCGI_ROLE is set to AUTHORIZER and FCGI_APACHE_ROLE is not set. The application must be defined as provider type authnz using AuthnzFcgiDefineProvider. The application is expected to handle both authentication and authorization in the same invocation using the user id, password, and other request data. The invocation occurs during the Apache httpd API authentication phase. If the application returns 200 and the same provider is invoked during the authorization phase (via Require), mod_authnz_fcgi will return success for the authorization phase without invoking the application. Example application:

#!/usr/bin/perl
use FCGI;
my $request = FCGI::Request();
while ($request->Accept() >= 0) {
    die if $ENV{'FCGI_APACHE_ROLE'};
    die if $ENV{'FCGI_ROLE'} ne "AUTHORIZER";
    die if !$ENV{'REMOTE_PASSWD'};
    die if !$ENV{'REMOTE_USER'};

    print STDERR "This text is written to the web server error log.\n";

    if ( ($ENV{'REMOTE_USER' } eq "foo" || $ENV{'REMOTE_USER'} eq "foo1") &&
        $ENV{'REMOTE_PASSWD'} eq "bar" &&
        $ENV{'REQUEST_URI'} =~ m%/bar/.*%) {
        print "Status: 200\n";
        print "Variable-AUTHNZ_1: authnz_01\n";
        print "Variable-AUTHNZ_2: authnz_02\n";
        print "\n";
    }
    else {
        print "Status: 401\n\n";
    }
}

Example configuration:

AuthnzFcgiDefineProvider authnz FooAuthnz fcgi://localhost:10103/
<Location "/protected/">
  AuthType Basic
  AuthName "Restricted"
  AuthBasicProvider FooAuthnz
  Require FooAuthnz
</Location>

Type authn, mechanism check_user_id

In this mode, FCGI_ROLE is set to AUTHORIZER and FCGI_APACHE_ROLE is set to AUTHENTICATOR. The application must be defined as provider type authn using AuthnzFcgiDefineProvider. AuthnzFcgiCheckAuthnProvider specifies when it is called. Example application:

#!/usr/bin/perl
use FCGI;
my $request = FCGI::Request();
while ($request->Accept() >= 0) {
    die if $ENV{'FCGI_APACHE_ROLE'} ne "AUTHENTICATOR";
    die if $ENV{'FCGI_ROLE'} ne "AUTHORIZER";

    # This authorizer assumes that the RequireBasicAuth option of 
    # AuthnzFcgiCheckAuthnProvider is On:
    die if !$ENV{'REMOTE_PASSWD'};
    die if !$ENV{'REMOTE_USER'};

    print STDERR "This text is written to the web server error log.\n";

    if ( ($ENV{'REMOTE_USER' } eq "foo" || $ENV{'REMOTE_USER'} eq "foo1") &&
        $ENV{'REMOTE_PASSWD'} eq "bar" ) {
        print "Status: 200\n";
        print "Variable-AUTHNZ_1: authnz_01\n";
        print "Variable-AUTHNZ_2: authnz_02\n";
        print "\n";
    }
    else {
        print "Status: 401\n\n";
        # If a response body is written here, it will be returned to
        # the client.
    }
}

Example configuration:

AuthnzFcgiDefineProvider authn FooAuthn fcgi://localhost:10103/
<Location "/protected/">
  AuthType ...
  AuthName ...
  AuthnzFcgiCheckAuthnProvider FooAuthn \
                               Authoritative On \
                               RequireBasicAuth Off \
                               UserExpr "%{reqenv:REMOTE_USER}"
  Require ...
</Location>

Additional examples

1. If your application supports the separate authentication and authorization roles (AUTHENTICATOR and AUTHORIZER), define separate providers as follows, even if they map to the same application:

   AuthnzFcgiDefineProvider authn  FooAuthn  fcgi://localhost:10102/
   AuthnzFcgiDefineProvider authz  FooAuthz  fcgi://localhost:10102/

   Specify the authn provider on AuthBasicProvider and the authz provider on Require:

   AuthType Basic
   AuthName "Restricted"
   AuthBasicProvider FooAuthn
   Require FooAuthz

2. If your application supports the generic AUTHORIZER role (authentication and authorizer in one invocation), define a single provider as follows:

   AuthnzFcgiDefineProvider authnz FooAuthnz fcgi://localhost:10103/

   Specify the authnz provider on both AuthBasicProvider and Require:

   AuthType Basic
   AuthName "Restricted"
   AuthBasicProvider FooAuthnz
   Require FooAuthnz

Limitations

The following are potential features which are not currently implemented:

Apache httpd access checker

The Apache httpd API access check phase is a separate phase from authentication and authorization. Some other FastCGI implementations implement this phase, which is denoted by the setting of FCGI_APACHE_ROLE to ACCESS_CHECKER.

Local (Unix) sockets or pipes

Only TCP sockets are currently supported.

Support for mod_authn_socache

mod_authn_socache interaction should be implemented for applications which participate in Apache httpd-style authentication.

Support for digest authentication using AuthDigestProvider

This is expected to be a permanent limitation as there is no authorizer flow for retrieving a hash.

Application process management

This is expected to be permanently out of scope for this module. Application processes must be controlled by other means. For example, fcgistarter can be used to start them.

AP_AUTH_INTERNAL_PER_URI

All providers are currently registered as AP_AUTH_INTERNAL_PER_CONF, which means that checks are not performed again for internal subrequests with the same access control configuration as the initial request.

Protocol data charset conversion

If mod_authnz_fcgi runs in an EBCDIC compilation environment, all FastCGI protocol data is written in EBCDIC and expected to be received in EBCDIC.

Multiple requests per connection

Currently the connection to the FastCGI authorizer is closed after every phase of processing. For example, if the authorizer handles separate authn and authz phases then two connections will be used.

URI Mapping

URIs from clients can't be mapped, such as with the ProxyPass used with FastCGI responders.

Logging

1. Processing errors are logged at log level error and higher.
2. Messages written by the application are logged at log level warn.
3. General messages for debugging are logged at log level debug.
4. Environment variables passed to the application are logged at log level trace2. The value of the REMOTE_PASSWD variable will be obscured, but any other sensitive data will be visible in the log.
5. All I/O between the module and the FastCGI application, including all environment variables, will be logged in printable and hex format at log level trace5. All sensitive data will be visible in the log.

LogLevel can be used to configure a log level specific to mod_authnz_fcgi. For example:

LogLevel info authnz_fcgi:trace8

AuthnzFcgiCheckAuthnProvider Directive

This directive is used to enable a FastCGI authorizer to handle a specific processing phase of authentication or authorization.

Some capabilities of FastCGI authorizers require enablement using this directive instead of AuthBasicProvider:

• Non-Basic authentication; generally, determining the user id of the client and returning it from the authorizer; see the UserExpr option below
• Selecting a custom response code; for a non-200 response from the authorizer, the code from the authorizer will be the status of the response
• Setting the body of a non-200 response; if the authorizer provides a response body with a non-200 response, that body will be returned to the client; up to 8192 bytes of text are supported

provider-name

This is the name of a provider defined with AuthnzFcgiDefineProvider.

None

Specify None to disable a provider enabled with this directive in an outer scope, such as in a parent directory.

option

The following options are supported:

Authoritative On|Off (default On)

This controls whether or not other modules are allowed to run when this module has a FastCGI authorizer configured and it fails the request.

DefaultUser userid

When the authorizer returns success and UserExpr is configured and evaluates to an empty string (e.g., authorizer didn't return a variable), this value will be used as the user id. This is typically used when the authorizer has a concept of guest, or unauthenticated, users and guest users are mapped to some specific user id for logging and other purposes.

RequireBasicAuth On|Off (default Off)

This controls whether or not Basic auth is required before passing the request to the authorizer. If required, the authorizer won't be invoked without a user id and password; 401 will be returned for a request without that.

UserExpr expr (no default)

When Basic authentication isn't provided by the client and the authorizer determines the user, this expression, evaluated after calling the authorizer, determines the user. The expression follows ap_expr syntax and must resolve to a string. A typical use is to reference a Variable-XXX setting returned by the authorizer using an option like UserExpr "%{reqenv:XXX}". If this option is specified and the user id can't be retrieved using the expression after a successful authentication, the request will be rejected with a 500 error.

AuthnzFcgiDefineProvider Directive

This directive is used to define a FastCGI application as a provider for a particular phase of authentication or authorization.

type

This must be set to authn for authentication, authz for authorization, or authnz for a generic FastCGI authorizer which performs both checks.

provider-name

This is used to assign a name to the provider which is used in other directives such as AuthBasicProvider and Require.

backend-address

This specifies the address of the application, in the form fcgi://hostname:port/. The application process(es) must be managed independently, such as with fcgistarter.