Apache HTTP Server Version 2.4

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# Apache Module mod_authnz_fcgi

Description: | Allows a FastCGI authorizer application to handle Apache httpd authentication and authorization
Status: | Extension
Module Identifier: | authnz_fcgi_module
Source File: | mod_authnz_fcgi.c
Compatibility: | Available in version 2.4.10 and later

### Summary

This module allows FastCGI authorizer applications to authenticate users and authorize access to resources. It supports generic FastCGI authorizers which participate in a single phase for authentication and authorization as well as Apache httpd-specific authenticators and authorizors which participate in one or both phases.

FastCGI authorizers can authenticate using user id and password, such as for Basic authentication, or can authenticate using arbitrary mechanisms.

### Topics

- Invocation modes
- Additional examples
- Limitations
- Logging

### Directives

### Bugfix checklist

- httpd changelog
- Known issues
- Report a bug

### See also

- Authentication, Authorization, and Access Control
- `mod_auth_basic`
- `fcgistarter`
- `mod_proxy_fcgi`

## 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

Description: | Enables a FastCGI application to handle the check_authn authentication hook.
Syntax: | `AuthnzFcgiCheckAuthnProvider provider-name|`None` option ...`
Default: | `none`
Context: | directory
Status: | Extension
Module: | mod_authnz_fcgi

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

Description: | Defines a FastCGI application as a provider for authentication and/or authorization
Syntax: | `AuthnzFcgiDefineProvider type provider-name backend-address`
Default: | `none`
Context: | server config
Status: | Extension
Module: | mod_authnz_fcgi

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`.